US2068126A - Process for refining motor fuels - Google Patents

Description

1937- O. FlTZ SIMONS ET AL PROCESS FOR REFINI NG MOTOR FUELS Filed Aug. 11, 1935 wv WW Jrwezztonxmm M mi sfi Mn wwdm Mm Mm OR L QE Patented Jan. 19, 1937 PROCESS FOR REFINING MOTOR FUELS Ogden Fitz Simons and Raymond A. Jack, Hammond, Ind., assignors to Standard Oil Company, Chicago, IlL, a corporation of Indiana Application August 11, 1933, Serial No. 684,694

1 Claim.

This invention relates to the solvent fractionation of motor fuel stocks or motor fuel fractions using ethanol as the selective solvent and more particularly to such processes in which subsequent distillation steps are used to partially dehydrate the ethanol. The invention also relates to processes for the production of improved ethanol-containing motor fuels. This invention furthermore includes apparatus in which the aforementioned processes can be carried out.

One object of our invention is to provide a solvent fractionation process for motor fuel stocks or motor fuel fractions to produce a rafiinate fraction and two extract fractions of different volatilities. Another object is to provide a process for the solvent fractionation of motor fuel stocks or motor fuel fractions with aqueous ethanol followed by the removal of all or part of the water by subsequent distillation steps. Another object is to promote removal of water in such a process by the addition of carrier substances. A still further object is to provide apparatus in which these various processes can be carried out. Other and more detailed objects will become apparent as the description of our invention proceeds.

Our invention in its various modifications can be understood most readily by describing it with reference to the drawing which is a conventionalized flow diagram illustrating a number of alternative processes and apparatus as preferred embodiments of our invention.

The supply tank ll contains aqueous ethanol. In general, the ethanol supply in tank II will be the constant boiling mixture of ethanol and water which contains approximately 95% ethanol. It is to be understood, however, that other concentrations of ethanol can be used, for instance, solutions having ethanol concentrations from 90% to 98%. All of these various solutions will be referred to in the specification and claim by the term aqueous ethanol. Solutions having ethanol concentrations substantially higher than that of the aqueous ethanol started with will be referred to as relatively anhydrous ethanol and solutions having substantially lower ethanol concentrations than that of the aqueous ethanol" started with will be referred to as dilute ethanol.

Aqueous ethanol from tank II is removed through valve I2 by means of pump l3, cooled if necessary in cooler l4 and introduced into downwardly directed spray l5 located near the top of countercurrent extraction tower l6. Simultaneously, a gasoline stock such as a pressure distillate, absorption plant naphtha, etc., is introduced at a suitable temperature through valve l1 from a source not shown into upwardly directed spray I8 located near the bottom of tower IS. The temperature or temperatures of the aqueous ethanol and gasoline stock introduced into tower l6 can be varied within wide limits to give the degree of extraction which may be desired. The desired temperatures will depend on the strength of the aqueous ethanol used, the type of stock being extracted, etc. In general temperatures from 20 to 80 F. and more particularly from 35 to 65 F. are suitable.

Aqueous ethanol introduced through spray l5 descends in tower I6 in countercurrent contact with a rising stream of gasoline stock from spray l8. Suitable baflies and/or agitation means can be used in tower I6 to promote thorough contact between the two materials. A raflinate phase is removed from the top of tower I 6' and will be discussed hereafter. An extract phase passes to the bottom of tower l6 and meets cooling coil H! which tends to throw out of solution the less desirable gasoline constituents of the extract, thereby promoting more thorough and efficient solvent fractionation.

The extract phase is removed from the base of. tower l6 through valve 20 and passes through heat exchanger 2| in which it comes in indirect contact with hot material as will hereafter be described. It is then introduced at an elevated temperature through line 2Ia into an efilcient fractional distillation tower 22 at an intermediate level therein. Tower 22 is provided near its base with reboiling coil 23 and near its top with dephlegmating coil 24. In the operation now being described reboiling coil 23 and dephlegmating coil 24 are operated at such temperatures as will permit the removal from the top of tower 22 of most or all of the Water introduced as part of the extract phase from tower Hi. This is made possible by the fact that the light hydrocarbons, particularly the light olefinic hydrocarbons, present in the gasoline stock have a pronounced azeotropic effect on the constant boiling mixture of ethanol and water and permit the removal in vapor form of all or most of the water together with only a portion of the total ethanol present. This azeotropic eifect is considerably enhanced if. the gasoline stock used is a pressure distillate and is still further enhanced if the pressure distillate is one produced by a vapor phase cracking process, since the olefinic hydrocarbons, such as are present in large proportions azeotropic effect than do the saturated hydrocarbons. .The temperature at which the top of tower 22 should be operated can be varied within wide limits and must be determined by experiment to meet the needs of the particular operation being conducted. In general, this temperature may be from 150 to 325 F. or preferably from 200 to 300 F. Such a temperature permits the removal from the top of the tower of light naphtha vapors together with all or most of the water and a portion of the ethanol. These mixed vaporsare condensed in condenser 25 and pass to separator 26. Due to the high concentration of water present the condensate from separator 26 separates into two liquid phases, the upper one being a light naphtha carrying in some cases a small amount of. ethanol and the lower one being a dilute alcohol 'of considerably lower ethanol concentration than the material in tank H. The lower layer is withdrawn from separator 26 through valve 2'! and introduced at an intermediate level into fractional distillation tower 28 provided near its base with reboiling coil 29 and near its top with dephlegmating coil 30. Tower 28 is operated with such bottom and top temperatures as to permit the removal of vapors representing the constant boiling mixture of ethanol and water from the top and removal of water containing little or no ethanol from the bottom. The ethanol concentration of the bottoms from tower 28 is generally suinciently low to make it desirable to send these bottoms to the sewer through valve 3|. However, they may be worked up by further distillation steps if their ethanol content is sumcient to warrant such a procedure. The constant boiling mixture of ethanol-water vapors is removed from the top of. tower 28 through valve 32 and condenser 33 to separator 34, fixed gases being removed through valve 35, and the condensate is recycled to tank I I through valve 36. Alternatively, valve 36 can be closed and the condensate recycled directly to the process through valve 31 and recycle line 38.

The upper layer from separator 28 is the light naphtha friction of the extract produced in tower I6. It is removed from the top of separator 26 by means of pump 39 and a substantial part of it is preferably recycled back to tower 22 through valve 40. This recycling increases the content-of light hydrocarbons, particularly light olefinic hydrocarbons, in the material entering tower 22 and promotes the azeotropic effect whereby water is removed. The remainder of the light naphtha fraction can be removed through valve 4! for further treatment or use as desired or it can be passed through valveTZ to mixer 43 where it is blended with the heavy naphtha fraction as will be hereinafter described.

The material removed from the base of tower 22 represents the heavy naphtha fraction of the extract from tower i6 and contains some substantially anhydrous or at least relatively anhydrous ethanol. This material is removed from the base of tower 22 through valve 44 by means of pump 45 and is passed through heat exchanger 2| where it gives up some of its heat to the material entering tower 22. From heat exchanger 2| the heavy naphtha can be removed through valve 46 for further treatment or used as desired, or, preferably, it can be passed through valve 41 to mixer 43 where it is blended with the light naphtha from separator 26 or other light naphtha to produce a balanced motor fuel. This motor fuel is a highly superior product since the low antiknock materials have been eliminated as raffinate in tower [6. Moreover, it contains some ethanol and this tends to enhance its antilmock value. The ethanol remaining in the finished motor fuel is, in most cases, substantially anhydrous, and therefore will remain in solution without separating from the rest of the motor fuel.

Returning now to the raflinate phase removed from the top of tower Hi, this passes through valve 49 and heater 50 into fractional distillation tower 5| at an intermediate level therein. Tower 5| is provided with reboiling coil 52 near its base and dephlegmating coil 53 near its top. This tower is operated at such a temperature that suL- stantially all of the water present passes overhead. This water carries with it the lighter hydrocarbons present and also much or most of the ethanol present. The mixed vapors pass oil. through valve 54, are condensed in condenser 55 and pass into separator 34 by way of valve 56. When the gasoline stock introduced to the process through valve ll contains light naphtha hydrocarbons, a portion of these will normally be present in the overhead from tower 5| and will thereby be recycled to the process. In many cases this is not in any way deleterious but if these light raflinate hydrocarbons build up to an undesirable extent they can be removed by adding water to the overhead from tower 5i, separating out the light naphtha materials as was done in separator 26 and redistilling the aqueous ethanol phase to recover the ethanol as was done in tower 2B.

The bottoms from tower 5i represent the heavy naphtha fraction of the raflinate and normally contain at least a small amount of substantially or at least relatively anhydrous ethanol. These bottoms can be passed through line 58 to mixer 59 where they can be blended with light naphtha introduced through valve or other light naphtha to produce a finished motor fuel which passes out through line 6| for further treatment or use as desired. This motor fuel will in general bemarkedly inferior to the motor fuel passing out of the process through line 48.

If it is not desired that the ethanol introduced into tower 22 be left in the heavy naphtha fraction of the extract at least a substantial part of this ethanol can be separated out by using a partial trap-out-plate 62 located at a suitable level above reboiling coil 23 and below the point of introduction of the extract phase. This level should be so selected that all or most of the ethanol can be removed by the trap-out-plate. Alternatively this material can be removed in vapor form. The ethanol thus withdrawn together with the accompanying hydrocarbon material passes through valve 63 and into stripping tower 64 at an intermediate level therein. Tower 64 is provided with reboiling coil 65 located near its base and dephlegmating coil 66 located near its top. This stripping tower is operated with such bottom and top temperatures that all or most of the ethanol passes overhead and bydrocarbon constituents are removed at the base, passing off through valve 61 and joining t. bottoms from tower 22. The overhead from tower 64 passes to condenser 68 and thence to separator 69, fixed gases being removed through valve 10. This material being high in ethanol can be removed through valve II for further treatment or use. Substantially anhydrous ethanol of a fair degree of purity can thus be produced. Alternatively, material from separator 69 can be passed through pump 12 to mixer 59 wherein 1| aoaaiae it is blended with the ramnate fraction from tower i. By this means the ethanol can be used to fortify the raflinate material. Thus a high antiknock extract can be produced directly and a high antlknock ramnate by blending with substantially anhydrous ethanol produced as a by-product of the refining of the extract.

Instead of using a complete gasoline pressure distillate, absorption plant" naphtha or other material containing light ends, the stock introduced into tower it, this stock may suitably be a heavy naphtha fraction, particularly a heavy naphtha fraction of a pressure distillate. Such a heavy naphtha may suitably have an initial boiling point of from 150 to 300 F. or preferably from 200 to 275 F. when operating on such a stock. the hereinbefore references to the light naphtha fraction are not pertinent and the azeotropic effect of the light gasoline hydrocarbons on the water removal must be obtained by other means. This can be done by introducing a carrier material" into the process through valve it from a source not shown. As.

such a carrier material, a narrow petroleum cut, preferably a narrow cut from a pressure distillate, particularly a vapor phase pressure distillate, is suitable. A narrow cut from an extract produced from a vapor phase pressure distillate by the use of a selective solvent is still more suitable. Such a out should have a boiling point substantially within the range 130 to 180 F. or preferably 140 to 170 F. and should have a maximum boiling point substantially lower than the minimum boiling point of the heavy naphtha stock introduced into tower it. Instead of a narrow petroleum cut of this type a pure hydrocarbon boiling in this approximate range can be used. An olefinlc hydrocarbon such as hexylene is highly suitable. Cyclohexane, hexane and benzol can also be used. When such a carrier is added it will pass ofi from the top of tower 22 along with the water and some ethanol and will appear as the top layer in separator 26 from which it can be removed by pump 30 and recycled back to the process through line see and valve at. With emcient fractionation and with a heavy naphtha stock having a minimum boiling point substantially above the boiling point of the carrier material there thus need be little or no loss of the carrier material.

An interesting feature of our process lies in the tact that although aqueous ethanol of a given ethanol concentration is introduced into tower it, the ratio of ethanol to water is generally somewhat .higher in the ramnate phase and somewhat lower in the extract phase than in the aqueous ethanol introduced. When operating on a heavy naphtha stock the result is that the overhead from tower 5! is relatively anhydrous ethanol and in the absence of low-boiling hydrocarbons it can be recovered as a. by-product, all or part of it being removed from the system through valve lid. Alternatively all or a large part of this ethanol can be left in the rafiinate, thereby increasing its antiknock rating.

Although we have described our process and apparatus in connection with certain embodiments thereof, we do not mean to be limited thereby since numerous modifications within the scope of our invention will occur to those skilled in the art.

We claim:

Process for refining a heavy naphtha motor fuel stock, comprising contacting said stock with aqueous ethanol, separating a rafilnate phase and an extract phase, adding a hydrocarbon carrier material boiling approximately within the range 140 F. to 170 F., fractionally distilling said extract phase together with said hydrocarbon carrier material to separate an overhead fraction comprising said hydrocarbon carrier material and dilute ethanol, condensing said overhead fraction, separating said dilute ethanol from said hydrocarbon carrier material, redistilling said dilute ethanol to produce a substantially constant-boiling mixture of ethanol and water, recycling said mixture back to said contacting step and recycling said hydrocarbon carrier material back to said first mentioned distilling step.

OGDEN FITZ SIMONS. RAYMOND A. JACK.

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