US2591672A

US2591672A - Dehydration of alcohols by gasoline extractive distillation

Info

Publication number: US2591672A
Application number: US68876A
Authority: US
Inventors: William E Catterall
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1949-01-03
Filing date: 1949-01-03
Publication date: 1952-04-08
Anticipated expiration: 1969-04-08

Description

April 1952 w. E. CATTERALL 2,591,672

DEHYDRATION OF ALCOHOLS BY GASOLINE EXTRACTIVE DISTILLATION v Q T I F l) (D A H QT 1.5g

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T m o (Jillian: E.Cattera-ZZ {Inventor bgwdbborneg April 8, 1952 w. E. CATTERALL 2,591,672

DEHYDRATION OF ALCOHOL-S BY GASOLINE EXTRACTIVE DISTILLATION Filed Jan. 3, 1949 2 SHEETS--SHEET 2 GASOLINE FEED 2 9 WATER ALcoHoL FEED i coHoL GAsoLmE T E LEND SOLVENT QEcvcL N L OJ tllzjam E. (fatter-all Invento b MM aLLorEEg- Patented Apr. 8, 1952 DEHYDRATION F ALCOHOLS BY GASOLINE EXTRAGTIVE DISTILLATION William E. Catterall, Elizabeth, N. .L, assignor to Standard Oil Development Company, a corporation of Delaware Application January 3, 1949, Serial No. 68,876

4 Claims. 1

This invention relates to the dehydration of alcohol or mixtures containing alcohol by means of extractive distillation employing gasoline as the extractive distillation solvent. The invention is also concerned with the production of gasoline-alcohol blends by a process wherein the alcohol is dehydrated by means of extractive distillation using as the solvent all, or a fraction of the gasoline into which it is desired to blend the alcohol.

It is an object of this invention to dehydrate neutral organic oxygenated compounds such as alcohols, kctones, ethers, or mixtures thereof. It is an object of this invention to dehydrate neutral organic oxygenated compounds such as alcohols, ketones, ethers, or mixtures thereof in such a manner that the dehydrated compounds become simultaneously blended in gasoline.

It is a further object of this invention to prepare a gasoline blend containing alcohols,

ketones, ethers, etc., or mixtures thereof. It .is-

also an object of this invention tofully and economically utilize the process streams resulting from a hydrocarbon synthesis operation.

Various processes are known to the art in which a mixture of hydrocarbons and organic oxygen containing compounds are produced. Some of these processes are: the low temperature carbonization of coal, peat and similar materials; destructive hydrogenation of coals, wood and shales; the methanol synthesis; the so-called oxo synthesis in which olefins are reacted in the presence of carbon monoxide and hydrogen; the numerous oxidation processes, particularly the oxidation of propane and other petroleum fractions; and the well-known hydrocarbon syn-- thesis operation. The products of the abovementioned reactions are usually numerous, but can be classified into two groups, namely, the hydrocarbons and the non-hydrocarbons, the latter including the alcohols and other oxygenated compounds.

It is well known that alcohols, ketones, ethers, etc., may be blended with gasoline and a suitable motor fuel thereby produced. Alcohols such as ethanol, isopropanol, n-propanol, etc., are usually obtained, particularly from the synthesis reactions mentioned above, as aqueous azeotropic mixtures which must be dehydrated before the alcohol can be blended with gasoline. This dehydration is normally carried out by azeotropic distillation using an entraining agentv such as ethyl ether, isopropyl ether, benzene, cyclohexane, etc. Such dehydration processes involve considerable cost and are uneconomlcal from a heat consumption standpoint. The pur pose of this invention is to provide an improved process for .efiecting the dehydration and at the same time recovering a blended gasoline from the dehydration operation.

According to the terms of this invention the dehydration of the alcohol or other oxygenated compounds employed in the gasoline blending operation is carried out by means of extractive distillation using as the solvent all or a fraction of the gasoline into which it is desired to blend the alcohol or other material. The process is particularly applicable in the hydrocarbon synthesis operation wherein the products separate into a hydrocarbon layer including gasoline and a water layer including alcohols, ketones, etc. In the overall process of recovery of synthesis products, the water layer is subjected to water extractive distillation to reject light materials such as acetaldehyde, propionaldehyde, ethyl acetate, and some acetone, followed by concentration of the remaining water layer by straight fractionation to reject the acids and the bulk of the water. The water layer which is now reduced toa concentrated alcohol-ketone mixture is then dehydrated by means of extractive distillation usingessentially all or part ofthe product gasoline stream from the synthesis plant as the solvent. In a typical synthesis plant based on natural gas, the final gasoline mixture would contain about 10 volume per cent oxygenated compounds.

Figure 1 represents a simplified flow plan of a typical process which describes one modification of the present invention. Referring to Figure 1, the numeral 1 represents a synthesis zone in which a mixture of hydrogen and carbon oxides is reacted in the presence of a catalyst such as sintered red iron oxide promoted with potassium carbonate. In the synthesis zone the reaction takes place'at atemperature of about 300 F. to 800 preferably at about 650 F., and at pressures in the range of 25 to 750 p. s. i., preferably about 400' p. s. i. The gaseous eiiluent leaves the synthesis zone via line 2, and is passed to a condenser and scrubber notshown, after which it enters separator 3. In separator 3', the condensed product separates into two phases, namely, an upper hydrocarbon phase 6,. and a lower water phase 4. The hydrocarbon phase is led via line 6 to fractionatorl, where there is taken overhead via line 8, material of the C4 and lighter range, while hydrocarbons in range of C5 and above are removed as bottoms via line 9 and introduced to treater it. Inthe treater It,

the hydrocarbons are treated in the vapor phase with bauxite or other cracking catalyst at a temperature of approximately 700 to 900 F. In the treater the mixture undergoes a mild. cracking during which any oxygenated compounds present are decomposed to hydrocarbons. The hydrocarbons also undergo isomerization and cracking which improve the quality of the material. The total vapor eiliuent is passed from the treater l via line H to fractionator 12. In fractionator 12, the hydrocarbons are separated into an overhead comprising C3 and lighter hydrocarbons, a gasoline side stream comprising the C4. and heavier materials boiling up to 430 F., and a bottoms boiling at 430 F. and above, which is removed via line I5. The light hydrocarbons emerging from fractionator I and I2 via lines 3 and I3 respectively, are passed to a polymerization zone wherein the olefins are polymerized to polymer gasoline by a typical polymerization process such as that carried out in the presence of the well-known UOP polymerization catalyst at a temperature of 300 to 500 F., and at a pressure of 250 to 2000 p. s. i. The resulting gasoline recovered from the polymerization is known as polymer gasoline.

Returning to the drawing, the water layer 4 is withdrawn from separator 3 via line It and introduced into extractive distillation column 18. In this column, the water layer is distilled countercurrent to internal liquid water reflux, which is introduced into the column .via line is. The water is introduced in amounts sufficient to insure the distillation of light neutral nonalcoholic oxygenated compounds from the water layer. To this extent, water in the amount above 50 mol per cent, preferably '10 to 80 mol per cent, is maintained in the liquid on the bulk or the plates in the extractive distillation tower. Sullicient water is added through line l9 to insure such water concentration. The distillate removed overhead via line consists of low boiling or water-insoluble materials such as acetaldehyde, propionaldehyde, ethyl acetate, methyl acetate, dimethyl acetal, some acetone, etc. The vapors are condensed in condenser 2| and removed from the system via line 22, however, part of the condensate is refluxed to column I8 via line 23. The bottoms from column l8, which now comprise an aqueous solution of the alcohols, acids, and higher molecular weight oxygenated compounds of other types, is removed via line 24 and introduced into concentrating column 25. This column is so operated as to remove overhead the alcohols and other neutral oxygenated compounds via line 26. The distillate is condensed in condenser 21, and removed via line 23 as feed to the dehydration column 32 as will be explained below. Part of the condensate is returned as reflux to column via line 29. Bottoms from the concentrating column comprise an aqueous solution of acids present in the original water layer, and these are removed to storage via line 30. However, a portion of the aqueous bottoms may be employed as the extractive distillation solvent entering through line l9. Open steam may be supplied to the bottoms of column l8 and 25 or reboilers may be provided.

This water extractive distillation method of eliminating compounds unsuitable for gasoline addition is only an example used for purposes of illustration. Other processing methods such as ordinary fractional distillation may be suitable for particular mixtures and will be apparent to those skilled in the art.

Referring now to the dehydration column 32, there is introduced thereto via line 28, an aqueous mixture of the alcohols originally present in the water layer together with any higher molecular weight neutral oxygenated compounds such as lretones, ethers, etc. Gasoline or fractions of gasoline are introduced into the dehydration column at a point near the top thereof via line33 Heat is supplied indirectly in reboiler 43. The dehydration column is operated in such a manner that the water present in the alcohol feed is removed overhead from the column. Sufficient gasoline is added to the top of the tower to permit withdrawing the gasoline from the bottom of the tower with the dehydrated alcohol. The necesary condition which must be met in the liquid mixture on substantially all the plates of the tower is that the water must be more volatile than the bulk of the solvent (as well as being*-.

more volatile than the alcohol) otherwise water will be withdrawn from the bottom of the tower with the solvent and alcohol. Complete removal of the Water will generally be assured by maintaining a minimum gasoline concentration in the liquid on the plates of the tower of at least 40mol per cent, for example, 40 mol per cent to 99 mol per cent, preferably above '70 mol per cent. Such concentrations permit the complete vaporization of the water and accomplish the withdrawal from the bottom of the tower of substantially anhydrous alcohols dissolved in the extractive solvent.

The hydrocarbon solvent added to the top of the tower and descending as reflux has very limited capacity to absorb either water or lighter alcohol such as ethanol from the ascending vapor, and therefore to avoid excessive carryover of alcohol into the overhead, the amount of vapor ascending the tower should be held close to minimum necessary to assure complete reinoval'of water from the bottoms. For the same reason, the hydrocarbon concentration usually remains high, for example, 96 to 99 mol per cent, above the feed. At the feed point, the feed mixes with the solvent and substantially decreases the hydrocarbon concentration in the reflux. It is the hydrocarbon concentration in the section of the tower below the feed point that is critical to the separation of water from alcohol, and it is in this zone that a hydrocarbon concentration of at least 40 mol percent, preferably above 70 mol per cent, must be maintained to assure a favorable relative volatility of water to alcohol.

It is to be understood that during the gasoline extractive distillation, some of the gasoline passes overhead via line 34 together with the water. The total overhead is condensed in condenser 35 and led to separator 36 wherein the condensate separates into an upper gasoline layer 37 and a lower water layer 38 which is removed from the system via line M. The gasoline layer may be refluxed to the column via line 39, or removed entirely or in part via line 40 with the blended gasoline leaving the column as bottoms via line 42. Part of the alcohol or other oxygenated compounds in the feed may also pass overhead. To recover the portion of such material which dissolves in the decanted water layer, this water may be recycled to column 25 via line 24 or other feed point.

The gasoline fraction obtained from fractionator i2 is an excellent source of solvent for the dehydration process and to this end thefraction may be removed via line H and led to column 32 where it enters via line 33. Polymer gasoline eral, a gasoline boiling in the range of 100 F. to 430 F., preferably 150 F. to 430 F. is suitable.

It is desirable that the vapor pressure of the gasoline used be'as low as possible to avoid the necessity of vaporizing excessive quantities of gasoline in the. distillation, which causes excessive heat consumption. Therefore, it is desirable to use a gasoline stock which does not yet have light ends such as C4 hydrocarbons blended in for vapor pressure requirements. Excessive light ends also serve to increase the amount of gasoline which must be withdrawn as overhead product to avoid the build-up of light ends in the upper section of the column. This withdrawal of hydrocarbon from the overhead decreases the net solvent downflow in the tower, and therefore decreases the solvent concentration and decreases the efiective. relative volatility of water to alcohol.

A relatively pure hydrocarbon such as diisobutylene, benzene or toluene might be used as the solvent, or a commercial mixture of aromatics such as motor benzol would be suitable. There will be some differences in the efiectiveness of the solvent depending on whether the hydrocarbon is predominantly paraifin, olefin, naphthene, or aromatic, but all hydrocarbon types are suitable. If a pure hydrocarbon or narrow-boiling fraction is used as the solvent, the boiling range should be above about 30 0., preferably above about 60 C., to avoid excessive solvent flow requirements and excessive heat requirements.

Although the invention has been described in regard to the dehydration of alcohols, the process isv equally applicable to the dehydration of mixtures of alcohols or to mixtures of alcohols with other neutral oxygenated compounds such as ketones, ethers, etc. The presence of any oxygenated compound suitable for blending into gasoline may be tolerated in the feed to the dehydration process. The invention is most advantaeously applied to the dehydration of individual or mixed C2 and C3 alcohols which form homogeneous water azeotropes, and thus cannot be readily dehydrated by straight distillation. The invention is also applicable to an alcohol mixture containing lower and higher boiling alcohols than those mentioned, although a large fraction of any methanol present would distill overhead due to its high vapor pressure and limited solubility in hydrocarbons. The process is particularly suitable to aqueous alcohol mixtures derived from the oxidation of light hydrocarbons Or from the hydrocarbon synthesis involving hydrogen and carbon monoxide. To produce a stable non-corrosive gasoline, it is necessary to remove the bulk of such non-alcoholic contaminants as acids, esters, and aldehydes. This removal is assured by the water extractive distillation step already outlined.

During the water extractive distillation operation as carried out in column [8, considerable amounts of acetone and methanol may remain in the bottoms removed from the water extractive distillation column. These volatile compounds would likewise concentrate in the overhead taken from the concentrating column and therefore would be present in the feed entering the dehydration column via line 28'. These materials would distill overhead to a large degree in the dehydration column and would then tend to accumulate in the dehydrating tower overhead stream if the decanted Water is recycled to column 25. This accumulation may not be disadvantageous unless it seriously interferes with phase separation. in the decanter. However, to prevent the concentration of large amounts of acetone and methanol in the dehydration column, it may be necessary to remove these components from the. system, for example, as an anhydrous stream from the top of concentrating column 25. In t is event, the remaining neutral-oxy compounds, including the alcohols, etc., would be removed as a side stream and then fed to the dehydration. column 32. Other methods of removing these components will be apparent to those. skilled in the art.

It has been ascertained that the concentration of the gasoline solvent has a definite efiect on the relative volatility (alpha) of Water to the alcohol being.v dehydrated. For example, the relative volatility of water to ethanol in 70 to mol per cent hexane solution was estimated to be within the range of 3 to 5. The steam requirement when operating with hexane under optimum conditions is estimated to be 6 to 10 lbs. per pound of water removed, which is very favorable compared to the 20 to 40 lbs. of steam required in conventional azeotropic distillation practice. The extractive distillation process has this strong advantage over azeotropic distillation because a much higher solvent concentration can be maintained below the tower feed point and a much better relative volatility in this critical region can be realized. In either case the solvent concentration is very high above the feed point and the relative volatility of water to alcohol is very high in this zone; however, the capacity of the solvent to reflux ethanol is limited, and it may require an undue solvent addition to avoid the presence of some ethanol in the overhead.

This process is particularly suitable for use when it is desired to produce an alcohol-gasoline blend or blending stock from the alcohol to be dehydrated. When the dehydrated alcohol in pure form is the desired product, it would be necessary to separate the alcohol from the hydrocarbon-alcohol mixture obtained from the bottom of the extractive distillation tower, and additional processing equipment would be required. This method would be considerably more expensive than the usual azeotropic dehydration method.

Under certain circumstances it may be desirable to use as the extractive distillation solvent a greater quantity of hydrocarbon than the alcehol is to be blended with. In this case by separate distillation of the bottoms mixture a portion of the gasoline may be recovered alcohol-free for recycling to the top of the extractive column. These two distillation operations can be combined in one tower to eilect an important heat economy as shown in Figure 2.

Referring to Figure 2 aqueous alcohol feed is introduced into tower I via line 2 at a point above the midsection of the tower while gasoline is introduced via line 3 at the top of the tower. The alcohol-gasoline blend is withdrawn as a liquid sidestream from the lower section of the tower via line 4 instead of from the bottom of the tower- Overhead vapors are removed via lin 5, condensed in condenser 6 and separated in decanter 1 into a gasoline phase which is refluxed to the tower via line 8 and an aqueous phase which is removed via line 9. Additional hydrocarbon iord'ecycle is withdrawn from the bottom via line I and returned to the gasoline feed line 3. The vapor supplied to the bottom of the tower via line 12 from the reboiler H serves both to strip alcohol from the hydrocarbon recycle in the lowest zone of the tower and to accomplish the extractive distillation in the higher zones.

Without attempting to explain the mechanism by which the desired separation of water occurs in the dehydration column, it can be said that the process is one of vapor-liquid extraction in which the vapors contain a greater concentration of water relative to the alcohol being dehydrated than under the normal fractional distillation conditions in the absence of the considerable amount of liquid gasoline internal reflux; It is evident from the results obtained'that the gasoline employed within the limits specified increase the effective vapor pressure of water in comparison with the vapor pressure of the alcohol being. dehydrated, thus allowing the water to pass overhead from the distillation zone. The temperature of the aqueous alcohol fed to the dehydration column is preferably close to the temperature of the liquid on the plate at the point of addition'of the feed, although it may be lower to partially condense vapors ascending to the feed plate. For continuous efficient operation the gasoline must be added continuously near the top of the column while the aqueous alcohol being' purified is continuously fed to the column at a lower point, and while suflicient heat is provided to afford di tillation throughout the column. The feed stream 1 may be preheated to a temperature close to that of the internal liquid gasoline reflux under equlibrium reboiling conditions at the point of introduction. The preheated aqueous feed may be liquid, partially vaporized, or completely vaporized when introduced into the extractive distillation column. Vapors of water and of the alcohol being dehydrated pass upwardly through the distillation zone in contact with descending internal liquid gasoline reflux under equilibrium reboiling and refluxing conditions.

The quantity of gasoline required to be introduced continuously at the top of the distillation sections of the tower under certain c-onditions, but no serious disadvantage *results from this situation if proper reflux flow down the tower can be maintained.

The gasoline employed as the extractive distillation solvent may be the gasoline produced in the hydrocarbon synthesis operation, the polymer gasoline recovered from the polymerization.

process described, benzene, motor benzol, or any gasoline or gasoline fraction produced extraneously, as for example, by catalytic cracking, thermal cracking, alkyiation, etc.

The dehydration tower may be operated at atmospheric pressure, under vacuum, or at superatmospheric pressures.

The invention is illustrated by the examples set out in the table. The table shows the results of experiments conducted in an extractive distillation column of 30 plates. In the experiments the aqueous alcohol was fed to the 15th plate and. the extractive distillation solvent to the th plate. The total vapor taken overhead Was condensed and two layers formed which were decanted. The hydrocarbon phase was refluxed, if desired, to the column while the aqueous phase was removed from the system. The hydrocarbon when employed as reflux was preheated prior to its return to the column. In the runs described benzene was employed in approximately 80 mol per cent concentration in the liquid reflux below the point of addition of the solvent and the catalytically-cracked naphtha in approximately 90 mol per cent concentration.

-- The alcohol feed was a blend bearing the following analysis:

A. ,On a wet basis zone for accomplishing the desired dehydration is Volume considerably greater than the quantity of conper cent densate with which it becomes homogeneously Alcohols 83.5 mixed on each plate in order to make the gaso Water 16.5 line concentration of the internal reflux substan- B. On an anhydrous basistially above a critical minimum in the range Ethanol 55.0 above 40 mol per cent. With adequategasoline 5s n-Propanol 32.0 concentration in the internal reflux for effecting n-Butanol 10.0 the dehydration, the alcohol being dehydrated is n-Amyl alcohol 3.0

TABLE Dehydration of aqueous alcohols by hydrocarbon extractive distillation OPERATING CONDITIONS Alcohol Feed Solvent Feed Hydm Temp. C. 0!

a bon Run lle flux Composition Material ccJln. fgga %!Z;

r10 .l C1-C5 Alcohol rs Benzene (so 510 180 65 Blend. mol per cent). 125 C2C5 Alcohol 69 Catcracked 940 0 67 56 Blend. Naphtha mol per cent).

1 Boiling range 47 C.198 O.

RESULTS Overhead Product Bottoms Product Per Cent Run Hydrocarbon Phase Aqueous Phase if fzgg fi Vol. For Weight A news P o t P c t m/hr' A1 i l i (gent Olgerhead or on er en co 0s a or (gm/hr Alcohols Alcohols 120 0 33 24 510 1 0.1 7.2 l25 365 ll 30 67 575 2 75 0. 1 35 What is claimed is:

1. A method of simultaneously dehydrating "aqueous alcohols to a fractional distillation zone at an intermediate point thereof, continuously adding hydrocarbon boiling in the gasoline boiling range of 100 F. to 430 F. as solvent to the fractional distillation zone at a point substantially above the aqueous alcohols feed point to maintain an internal liquid reflux having a gasoline hydrocarbon content in the range above 70 mol per cent below the point of addition of the gasoline hydrocarbon, distilling from said aqueous alcohols a vaporous mixture comprising water wherein the distilled vaporous mixture flows countercurrent to the gasoline hydrocarbon reflux, withdrawing a dehydrated mixture of gasoline and C2 to C5 alcohols as a lower sidestream from the fractional distillation zone, and withdrawing gasoline hydrocarbon substantially free of water and alcohols as bottoms from the fractional distillation zone.

2. The method of claim 1 in which the gasoline hydrocarbon substantially free of water and a1- cohols is recycled as solvent to the fractional distillation zone.

3. A method of simultaneously dehydrating a mixture of aqueous alcohols containing 2 to 5 carbon atoms per molecule and preparing an alcohol-gasoline blend therefrom which comprises continuously feeding the aqueous alcohols to a fractional distillation zone at an intermediate point thereof, continuously adding hydrocarbon boiling in the gasoline boiling range of 100 F. to 430 F. to the fractional distillation zone at a point substantially above the aqueous alcohol feed point to maintain an internal liquid reflux having a content of said hydrocarbon in the range above 70 mol per cent below the point of addition of the gasoline hydrocarbon, distilling from said aqueous alcohols a vaporous mixture comprising substantially all the water present in the aqueous alcohols wherein the distilled vaporous mixture flows countercurrent to the gasoline hydrocarbon reflux and withdrawing a dehydrated solution of alcohols containing 2 to 5 carbon atoms in said gasoline hydrocarbon from a lower portion of the fractional distillation zone.

4. A process for recovering a blend of gasoline with alcohols and ketones from the reaction product obtained in the hydrogenation of carbon monoxide, said product containing hydrocarbons, acids, and neutral oxygenated compounds comprising aldehydes, ketones, alcohols, and esters which comprises separating the product into an oil phase and a water phase wherein each phase contains at least a portion of said hydrocarbons, acids and neutral oxygenated compounds, distilling the water phase in a water extractive distillation zone wherein the distilled vapors ascend countercurrent to an internal liquid reflux having a water content above mol per cent, removing as a distillate from the water extractive distillation zone a mixture containing hydrocarbons and neutral non-alcoholic oxygenated compounds including aldehydes, esters and a portion of the ketones, removing as bottoms from the water extractive distillation zone an aqueous acid solution of alcohols and the remainder of the ketones, stripping an aqueous solution of alcohols and the ketones from the aqueous acid solution, separating a gasoline fraction boiling in the range of F. to 430 F. from said oil phase, distilling the aqueous solution of alcohols and ketones in a second extractive distillation zone wherein the distilled vapors ascend countercurrent to an internal liquid reflux having a content of said gasoline, above 70 mol per cent, removing as distillate from said second extractive distillation zone a mixture comprising essentially all the water, and recovering as bottoms from the second distillation zone a blend of said gasoline and said alcohols and ketones substantially free of water.

WILLIAM E. CATTERALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,412,233 Ellis Apr. 11, 1922 1,420,006 Whitaker June 20, 1923 1,474,983 Schreiber Nov. 20, 1923 2,012,199 McElroy Aug. 20, 1935 2,290,636 Deanesly July 21, 1942 2,339,160 Dunn et al Jan. 11, 1944 2,371,010 Wolfner Mar. 6, 1945 2,379,110 Souders June 26, 1945 2,426,705 Patterson et al Sept. 2, 1947 2,467,966 Clark Apr. 19, 1949 2,470,782 McGrath et al. May 24, 1949 2,472,219 Lyons June 7, 1949

Claims

1. A METHOF OF SIMULTANEOUS DEHYDRATING AQUEOUS ALCOHOLS CONTAINING 2 TO 5 CARBON ATOMS AND PREPARING AN ALCOHOL-GASOLINE BLEND THEREFROM WHICH COMPRISES CONTINUOUSLY FEEDING THE AQUEOUS ALCOHOLS TO A FRACTIONAL DISTILLATION ZONE AT AN INTERMEDIATE POINT THEREOF, CONTINUOUSLY ADDING HYDROCARBON BOILING IN THE GASOLINE BOILING RANGE OF 100* F. TO 430* F. AS SOLVENT TO THE FRACTIONAL DISTILLATION ZONE AT A POINT SUBSTANTIALLY ABOVE THE AQUEOUS ALCOHOLS FEED POINT TO MAINTAIN AN INTERNAL LIQUID REFLUX HAVING A GASOLINE HYDROCARBON CONTENT IN THE RANGE ABOVE 70 MOLE PER CENT BELOW THE POINT OF ADDITION OFTHE GASOLINE HYDROCARBON, DISTILLING FROM SAID AQUEOUS ALCOHOLS A VAPOROUS MIXTURE COMPRISING WATER WHEREIN THE DISTILLED VAPOROUS MIXTURE FLOWS COUNTERCURRENT TO THE GASOLINE HYDROCARBON REFLUX, WITHDRAWINING A DEHYDRATED MIXTURE OF A GASOLINE AND C2 TO C5 ALCOHOLS AS A LOWER SIDESTREAM FROM THE FRACTIONAL DISTILLATION ZONE, AND WITHDRAWING GASOLINE HYDROCARBON SUBSTANTIALLY FREE OF WATER AND ALCOHOLS AS BOTTOMS FROM THE FRACTIONAL DISTILLATION ZONE.