US2436502A

US2436502A - Furfural recovery

Info

Publication number: US2436502A
Application number: US576856A
Authority: US
Inventors: Buell Charles Keith; Charles F Weinaug
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1945-02-08
Filing date: 1945-02-08
Publication date: 1948-02-24
Anticipated expiration: 1965-02-24

Description

B. K. BUELL. ETAL Feb, 24, wa

FURFURAL RECOVERY Filed Feb. a, 1945 s sheets-sheet 1 Feb. 24, 1948.-

B. KQ BUELL ETAL FURFURAL RECOVERY 3 Sheets-Sheet 2 Filed Feb. 8,- 1945 INVENTORS c.F. WEIN/mc;4 cK BUELL ATroRNEYs; 7

Feb. 24, 1948.

B. K. BUI-:LL ETAL. 2,436,502

FURFURAL RECOVERY .'Fled Feb. 8, 1945-' 3 .Sheets-'Sheet 3 m mi CF. WEINAUG CK. BUELL hv ATTORNEYS mmJOOU INVENTORS HOLVNOI .LOVtL-I Patented Feb. 24, la`948 UNITED STATES PATENT lOFFICE f 2,436,502 v FURFURAL RECOVERY charles Keith Bueil and .charles Borger, Tex., assignorsjto" Phillips Petroleum Company,

a corporation of Delaware Application February 8, 194,'5, Serial No. v5'7`6,856 y 2 Claims. (Cl. 26o-347) The invention relates to the recovery of furfural from admixture with hydrocarbon contaminants.'

For example, furfural used as an extractive'distillation solvent in esses may accumulate others, small quantities of hydrocarbon impurities, having a lower volatility than Cis, which have not been completely eliminated in preparhydrocarbonrecovery proc-- contaminants which may result in reducing the effectiveness of the furfural ing the C4 concentrate, enter the furfural system,

or low volatility hydrocarbons Ymay be 'generated in the furfural extraction system by polymerization or other reaction mechanisms, or such relatrance into the furfural system through valve, compressor, pump, etc., lubricating devices. These contaminants will hereinafter be referred to as oils.

Generally, if these oils are kept at a concentration below about one weight per cent the foaming of the furfural in the extractive distillation '20 tively non-volatile hydrocarbons may gain en"' and stripping steps will not be excessive. The

present invention provides a method for main-" s taining the level. These oils generally are not readily reconcentration of such oils atl a low moved from furfural by ordinary means, such as fractional or steam distillation, because they furfural so that separation by ordinary fractional distillation to obtain a pure fur-v fural or pure oil concentrate is impractical if not impossible.

We have found that water extraction can be used effectively for separation of furfural from contaminating oils. Our invention provides a has for its principal obimproved method of recovering furfural from hydrocarbons such as oils of the type described above.

to provide a suitable method this by means of water extraction. Another object is to accomplish this result with a minimum of equipment investment and inv a simple land- Another object is azeotropes with the furfural or boil.

of accomplishing distilled to recover dissolved and substantially furfural- I.easily controlled manner. Another object is to provide such a method which is appl1cable to the oilfurfural mixture obtained by the Vextraction of oil-contaminated furfural with a light hydrov .carbon solvent and evaporation or distillation of the solvent from the extract phase, as disclosed irr U. S. Patent 2,414,402, to Thodos et al., which issued January 14;"1947.' "Numerous other objects vof the present invention will more fully herein- .after appear. Y

In the accompanying drawings:

Fig. 1 portrays diagrammatically one arrangement of equipment used in a two-step Awater extraction process in accordance'with the present.

rinvention. Fig, 2 shows an arrangement Yin which the water extraction is conducted countercurrently in an extraction column. Fig. 3 shows a modified arrangement in which provision is made for preliminary concentration of the furfuralhydrocarbon mixture.

'It is disclosed in the copending application of Thodos and Weinaug, above -ident1ed, that foaming oils'lnay be removed from iuriural conta-minated therewith by liquid-liquid extraction :with a, hydrocarbon solvent immiscible with furfural whereby the foaming oils dissolve in the hydrocarbon, and separation of the hydrocarbon phasey from the resulting furiural phase. The furfural phase (raffinate) may be fractionally hydrocarbon solvent. ihe hydrocarbon phase (extract) may likewise be distilled to recover the which may be recycled to the extraction, leaving a residual mixture of the foaming oils and fur- ;fural. V'Ihe process of the present invention may be applied to such a residual oil-furfural mixture to enable tne recovery of the valuable furfural content thereof in uncontaminated form.

:In accordance with our invention the furfuralcil, mixture is first extracted with water in amount suicient to dissolve most or substantially all of the furfural. The amount of water required will depend upon the concentration of furiural in the mixture being extracted, the concentration hydrocarbon solvent prevailing in the eX- amount of water extractant used is such that the resulting aqueous phase ls considerably less than saturated (say not over 50% down to 25% saturated) with furfural under the extraction conditions. Often the concentration of furfural in the aqueous phase is less than 10 or even 5 weight per cent. The amount of water employed greatly exceeds the proportion. of Water in. the azeotrope of furfural and water so that a high temperature is not required in order to keep the aqueous phase as a single phase and so that in the subsequent fractional distillation of the aqueous phase the azeotrope will go overhead leaving Water as 'abottom product. It will be understood; that by using such an amount of water. that the resultingy to furfural under the extractionconditionsa bet. ter recovery of furfural is attained'A since the equilibrium ratio of furfural dissolved'` in. the..` water to furfural dissolved in the oil is greater with greater ratio of. water tooil. In generaLit f is preferred.. that the aqueousphase ofV furfurai and water resulting from the. extraction be notv over 50% rangingv downwardly toabout 25% of saturation. The. solubility of furfural. in water depends upon the temperature. Mains. (Chem.

Met. Eng. 2,6, 779 (1922).) gives-the following data;

Usually sufficient water is employed-.that the re-A 2,4seguo2 4 ture, usually ranging from atmospheric to moderately superatmospherc. The extraction is generally conducted in closed pressure-resisting equipment in order to minimize losses by volatilization.

The water extraction may be carried out in any suitable way, for example, by intimately mixing the' water and furlural-oil` mixture in a mixing pumporother adequate mixing means and then l0 allowing the mixture to separate into two phases or. layers in a settling zone or chamber or by continuously. countercurrently contacting the water extractant and the furfural-oil mixture in a column. equipped with contacting means such as 15. bubble caps, packing, etc. The operation may be extract phase is far from saturated with` respect justed in. accordance with-theprinciples herein disclosed that theramnate does not contain more than 3 weight per centof furfural and so that 35;-the-extract phase contains considerably less than (LL weightper cent of oil.v The former limitation insuresv aga-instiexcessive loss of furfural and the latter specication insures that the puried urfural product contain not over 0.1 weight per :qi cent of hydrocarbon.rv

The waterefurfural phase is .then subjected to fractional distillation to. separate the azeotrope of. fllrfuraland:water` overheadfrom a bottoms product ,composed essentially of theremainder of the water. which is recycled to the Water extraction unit in order to. save water and the small amount of` furfural which may be left therein. The. overhead; vapors are cooled andtotally condensed and the condensate caused to form two sulting aqueous phase containsanotmoreithan 5%; 4m. separate liquid layers; The'upper aqueous layer and frequently not. more than 3%. bltl weight of dissolvedl furfural.. TilsegofanA excessive. amount` of water inthe extraction stepzls citen undesirae. ble because the. heat consumption inthesubse.

istotally refluxed to the azeotrope column while the lower layer constitutes the oil-free furfural product of the. invention.

If desired, a smallV continuous` stream of the quent. azeotropc. distillation.` sten applied. to thec lean furfural from an extractive distillation-stripovery 15.0. degrees F;, sinceas: is explained above much .better recovery of furturalfrom oil is-there by. obtained, the loss.` of `furtural;A in. solution inV the oil phase being at.- a minimum. Another advan tage of the use ofa largexamount of'water, sothat l a dilute. aqueous-phase withY respectto f-urfural. results. is; that-.the solubilityo oil-l irr such adi lute@v aqueous phase-is-very low-wwhereaslos.v the aqueous phase becomes. saturated` with- Furfurallthe solubility of oil` therein increases Anotheradvantage of the mooi-moderate temperatures,

pingzone may he treated-in: accordance with the presentv invention, being water-extracted and the purified furfural being recovered from the resultant=furiural'-water; mixture and continuously remifturned` toithe fini-.uralextractive distillation zone.

However,v it i's generally desirable. to firstconcentrate the. oils since they represent only a small percentage ofthe turfural in a furfural extraction zrme.v Without firstL concentrating these oils an. 5.1i. excessively.V large.- volume: of 'water would be required: to extract the furiural and excessivelylargeiamounts: or heatwouldl'be` required in concentrating the.v furiural in the` resultant furfural` water mixture. Concentration of these7 oils can lifbei accomplished by fractionation. Apparently,

the previously suggested'V azeotropes'Y of furural and oils'. if actually formed, are of the minimum boiling. type. This, coupledwith the fact that the/.w1l oilsfboil` close to rurfural, but usually at a 055- slightly lower temperature,V makes it possible to prepare a concentrate of these oils but-impossible to effect complete separation between the furi'ural and? oils. by fractionation. Inl other words, the oils; plus some: furfural; can beV removed b y-fraci. ea. not over 150; degreesR, is that; the amount. mytionationias an; .overhead product leaving. a re1aor oil czlissolved` in, the. aqueousfphase is: minimized since thesolubility or oilixnaqueous-furiural. rises; with! increasing temperature.

The pressure at. which theextraction is con-- ducted. may depend'- son'lewhatv on?. the-l tempera.-

tivelyoi'lz-'f-ree-furfuralbottom product. This can be usedi as; .methodi` for: removing oils from furfu-ral but. is. not satisfactcrybecausefit necessarily' resultsfirrhieh furliurallosses.-y Byusing the water lit;A extractiommethodi cit-.mir invention in` conjuncaascoa 5. tion with an oil concentration step of this type, substantially complete removal of oil contaminants from furfural can be eiected without the furfural loss which would be involved in an attempt to use fractional distillation only.

By .water extracting the oil concentrateprepared as just described the furfural can be reg-- moved from the oil. Two liquid phases result from such treatmentja water-furfural rich phase and a hydrocarbon-oil rich phase. These phases can be collected separately, thereby effectively removing the oils from the furfural. The waterfurfural rich phase is then fractionally distilled*y to recover the furfural-water azeotrope as the overhead product and water as the bottom product. By condensing and cooling the overhead product, two liquid phases are obtained, a furrural-rich phase with only a small water anda water-rich phase with a small percentage of furfural. The two phases are separated from each other. The water-rich phase is totally refluxed to the fractionation column. They furfural-rich phase constitutes the puriied furfural product which may be returned to the furfural extractive distillation and stripping zone of the hydrocarbon recovery process for which the fvurfural is being used or further processed, stored, etc. This furfural product contains a small percen'lge ofrwater. However, this is usually advantageous since a small percentage of water is generally maintained in furfural used in the extractive distillation of light hydrocarbons in order percentage of to lower the boiling point of the furfural andy thereby decrease the tendency for furfural polymer formation in the extractive distillation and stripping steps. A further advantage is that the selectivity of the furfural for extractive distillation purposes is increased by the presence of small amounts of water. The use of furfural con. taining dissolved water in the extractive distillation of C4 hydrocarbons (butene and/or butadi-v ene) is described in the U. S. Patent 2,434,796, issued to Hachmuth on January 2), 1948. n

. The bottom product of the fractionator in which the water-furfural phase is distilled consists primarily of water the water extraction zone.

` If the contaminating hydrocarbons have reached a high concentration, the hydrocarbonfurfural mixture is often rst subjected to fractional distillation to remove without furfural loss as much as possible of any hydrocarbons boiling below furfural but above the hydrocarbons for whichthe furfural was used as a solvent extraction agent. This concentrates the furfural but does not remove the hydrocarbons having boiling points close to 'that of furfural. furfural concentrate with a suicient amount of water to dissolve the furfural,

phases, the lower phase being furfural saturated withwater and the. upper layer being water saturated with furfural at the existing temperature conditions in the overhead product ac :umulator.4

'Ifhcwater-rich phasenis used tolrefiux the co1-` and may be recycled to By mixing this as before, and I' allowing to settle, two liquid phases result. By

furfural-water azeotrope as Water as the bottom j The furfural-water azeotrope is con-l densed and-cooled as before giving two liquid l.

' it will usually be desirable to subject this product -introduced into cooler Normally furfural-recovered by -this method will..

contain about Gffweight per cent Water. If dry; furfural is desired furtherl processing will be necessary. However, for butadiene or butylenere-v covery it has been found advantageous to use furforal containing about 4 to 8 weight per cent of, dissolved water. The bottom product from the furfural-Water fractionator, consisting of Water, may be used in; the step wherein .the 'contaminated furfural is dissolvedin water.

The hydrocarbon' product from the settlingj zoneused in the water extraction of the furfural, the upper phase, maybe discarded or furtherv processedgl-Iowever, it-wil1 usually still containiappreciable amounts-of furfural. Consequently,

to a second water extraction step, in which case; the water .from th-e bottom of the furfural-water fractionator may be used as the extraction agent. The hydrocarbon-wat'er-furfural this second extraction step is all-owed to settle. Two liquid phases separate, one consisting primarily of hydrocarbon with only small amounts of dissolved furfural and the otherconsisting of water with the yfurfural recovered from the hy*-v drocarbon. The hydrocarbon phase isvremoved from the system for disposaL-storage, or further;- processing,etc. The Water phase containing the small amounts of furfural recovered from the4 hydrocarbon may be used as the water extraction agent in the rst extraction zone,

The mixture of .furfural and hydrocarbon treated inv accordancewith the, present invention v preferably contains about 20 weight per cent of hydrocarbon, -the balance being furfuraL, It the mixture contains less hydrocarbon than this it mixture from also introduced int'o mixer or centrifugal pump 4i by means of lines 2 and 3. In pump e the water and furfural are intimately mixed and discharged into-settler .6A by, means., of line 5.'

settler 6 two ,liquid phases separate,` the' tupper phase rich lin,:hydrocarbon and the lower phase rich in water dand 'furfural The lighter on neri phase'iows. over tiertical baille 6A in settler 6 g thereby separating;- theryheavier water-furfural mixture from. the 4lighter oil contaminant mixxture.' The oil-fcontaminantfis removed from settier tl through line 1. ,I The Water-furfural mixture' is ,removed from settler -6 and introduced into fractionator 9 throughline 8.

tor 9 the water-furiural mixture is In fractiona- I; fractionated .z

to obtain the water-furfural azeotrope as the overhead product .and substantially all water as" the bottom product.

removed fromcolumn .1H where the .product is,l totally condensed and The overhead product is 9 by means of line I0 and Y cooled, From cooler Hyg the liquefied andv cooled product is introduced-s into overhead-product of line I2.-

accumulator I3 by means' Iwo'.liquid-phase separation occurs `in accumulator 1,3...the :upper phase being a :les

ther V"processed, etc. Frequently ltiwil'l 15e-:desirable to subject it to another or 'more stages 'of extraction with Water to'remove the nal traces of furfural.

The Water-iuriural extract from the bottom o'f tower -2 is fed by means of line 28 `to fractionator 9. In tractionator 9 the furfuralewat'er aze'otrope fis obtained as-the overhead product which isconducted by means of'line Hl'to condenserand cooler v'Il to totally condensethe overhead prodnot. The cooled condensate `from Il i's -intr`o=l duced by means of line I2 into accumulator I3 and allowed to settle. 'Two lquidphase'sseparat in 13, -a furfural-rich and a water-rich phase.y The v'total water-rich vphase is supplied to "fractionator -9 as reuxby means vof line f5. The furfural-rich phase is removed ffrom accumulator li'through line i4 asthe'purifled furfuralproduct which Vmay Vbe sent to storage, further processinig, or returned to the extractiva distillation and stripping -zones of a 'hydrocarbon recovery p-l'GeSS.

'Thebottom product from i'actionator -9 `'con-'- slsts primarily of water and is `removed through line i6. This water may be discarded -from the system through drain line A"Il -or recycled -to the extraction -zone v25 by means Iof lines i8 and v21. Usually it lWill be desirable to recycle the water from fractionator 9 to the Water-extraction zone 26.

Line IS connecting with I8 -is provided, as in Fig. `1, for adding Water vto the system. Generally, a small amount of Water will have to be continuously added to the system to make up for the small amounts carried out in solution or entrainment with the hydrocarbon "and urfural products.

The modification of Fig. 2 `is not applicable 'to oil-'furfural mixtures more dense than Water, even though the water be :introduced at the bottom o`f tower 2 and the oil-furfural mixture at the top. In this arrangement, at some Vpoint in the process of extractio the density of the 'incompltely 'extracted ol-furfural mixture and the resultant water-furural mixture will become equal and no 'further contacting Will'occur.

In Fig. 3, f urfural containing hydrocarbon cone tarninant .is Afed to fraction'ator 3l toconcentrate thefurfural by `removing hydrocarbons boiling at a, lower' temperature than Vfurfural, but at a higher temperature 'than the hydrocarbons for which the furiural was 'used as a Aselective solvent. The "fractionator operated such that 'substantially lall of the ful-` fural is 'retained 'in the virettle product. The' hydrocarbon overhead `product vis condensed and collected inV accumulator `32. A portion of the hydrocarbon is used as reux to vthecolumn and the remaining portion is removed'from'the'system 'for 4storage,. disposal, or further processing, etc.

Ir -there iis Water present in the furfural feed to the column at least a portionf itwill constitute a 'part of the overhead product, in which case two 'liquid phases will separate in accumulator 32. The Water phase may be discarded or returned to the system inthe extraction zone to recover -any furfural therein. The 'bottom product from tower 31 passes 'via line '33 through cooler 4345 and is intl mately mixed'with Water'from line '35 insufficient quantity to dissolve the iuriural. 'The waterfurfuralihydrocarbon mixture i's 'introduced into extraction Lsettler 36 and allowed Ato separate into two rliquid phases, the upper 'phase being rich "in is usually 'preferably that might be retained 9 and water. The water-furfural phase is fed via line 31 to fractionatcr 38. In fractionator 38 furfural-water azeotrope constitutes the overhead product.

liquid phases separate, the lower phase being furfural saturated with water at the temperature of the accumulator and the upper phase being water saturated with furfural at the accumulator temperature. The water-rich phase is totally refluxed to column 38. 'I'he furfural-rich phase is the puried furfural product which is withdrawn from the system and sent to storage, or returned to the butadiene recovery step, essed for water removal, etc.

The bottom product of fractionator 38 consists of water primarily. This water is recycled Via line 40 and cooler 40A to extraction settler 4|. The function of extraction settler 4| is described hereafter.

The hydrocarbon phase from extraction settler 38 usually will still contain appreciable amounts of furfural. Consequently, it is desirable that this product be subjected to a second water-wash to recover the last traces of furfural. Hydrocarbon product from 36 is thoroughly mixed with Water, the bottom product from fractionator 38, and introduced into extraction settler 4|. Two

The overhead product is totally condensed and collected in accumulator 39. Two

or further procv'lli liquid phases separate in 4| a water-rich phase with a small amount of furfural constitutes the bottom layer and hydrocarbon with a relatively low furfural content constitutes the upper layer. The lower layer from extraction settler 4| is recycled as the water extraction agent via line to extraction-settler 36. The hydrocarbon upper layer was withdrawn via line 42.

Example Using the equipment of Fig. 3, furfural containing 81.5 weight per cent hydrocarbon was fed to fraetionator 3|. A temperature of 310 F. was maintained at the bottom of the fractionator and 188 F. at the top. 'I'he overhead product accumulator 32 was maintained at 100 F. The overhead product had the following composition: 99.0 Weight per cent hydrocarbon and 1.0 weight per cent furfural. A portion of the overhead product from fractionatcr 2 was returned as reux. A reiiux ratio of about 1.8 to 1, based on the overhead product, was maintained. The overhead make was removed from the system. The bottom product consisted of 70.0 weight per cent hydrocarbon and 30.0 weight per cent furfural. This product was cooled to about 100 F. and mixed with suincient water to dissolve most of the furfural and introduced into extraction settler 36. Two liquid phases separated, the upper layer rich in hydrocarbon and the lower layer rich in water and furfural. The upper layer had the following composition: 88.9 weight per cent hydrocarbon and 11'.1 per cent furfural. The lower layer consisted of 2.5 weight per cent furfural and 97.5 weight per cent water. The water-iurfura1 layer was fed to fractionator 38 where the furfural-water azeotrope was taken overhead and water out the bottom. A bottom temperature of 212 F. and a top temperature of 208 F. was maintained in fractionator 38. Fractionator 33 and its overhead product accumulator 39 were maintained at substantially atmospheric pressure. The overhead product was condensed and cooled to 100 F. In accumulator 39 two liquid phases separated; the lower phase consisted of 93.2 weight per cent furfural and 6.8 weight per cent Water and the upper phase consisted ci 8.0 weight per cent furfural and 92.0

10 weight per cent water. 'I'he upper phase was totally refluxed to column 38. The lower phase constituted the purified furfural product which was removed from the system.

The bottom product from fractionator 38, consisting of 0.025 weight per cent furfural and 99.975 weight per cent water, was cooled and mixed with the hydrocarbon product from extraction-settler 36 to remove most of the furfural remaining in the hydrocarbon product. This mixture was then introduced into extraction-settler 4|. Two liquid phases separated in extraction-settler 4|, an upper phase rich in hydrocarbon and a lower phase rich in water and furfural. The upper phase, consisting of 97.9 weight percent hydrocarbon and 2.1 weight per cent furfural, was removed from the system. The lower phase, consisting of 0.7 weight per cent furfural and 99.3 weight per cent water, was recycled to be mixed with the bottom product from fractionator 3| as the water extraction agent and subsequently introduced into extraction settler 36.

Generally, itwill be desirable to maintain a slight positive pressure throughout the system to prevent the possibility of air leaking in and pro moting furfural polymerization. High pressures are undesirable because of the high temperatures that would be required in the fractionation sys; tem thereby promoting furiural polymerization Where the desired pressures cannot be attained at the operating temperatures such as in the over-l head product accumulators on the fractionators', the extractionfsettlers, etc., residue gas may be used for pressuring and maintaining pressure on these vessels.

Forexample,- in operating according to the above described procedure, the pressure inace' cumulator 32, wl'ien totally condensing the over-1 head product from fractionator 3| and cooling to F., may actually be below atmospheric. Consequently, in order to prevent the possibility of drawing air into the accumulator a pressure of about 10 pounds gage was maintained by introducing residue gas into the accumulator. Pressure was maintained on the extraction-settler 35 by the same means. Extraction settler 4| was operated liquid full. Column 38 and accumulator 39 were operated at substantially atmospheric pressure. However, to insure against air leaking into the system a blanket of residue gas at a very slight positive pressure was maintained in accumulator 39.

It is to be understood that there are several possible modifications of this invention, among which are use of a larger number of steps of water extraction than described. In some instances it may not be necessary or desirable to employ the fractionation step performed byfractionator 3| of Fig. 3, especially in cases where the furfural concentration of the product to be purified is high or the concentration of the relatively lighter hydrocarbons is low.

' From the foregoing many advantages of the process of the present invention will be apparent to those skilled in the art. Principal among these advantages is the excellent recovery of furfural made possible by the present process. Other advantages are the simplicity, ease of control and economy of the process and the small amount of relatively simple and not unduly expensive equipment required. Another advantage is that the conditions in the several steps of the recovery process are readily `adjusted by the operators so as to minimize loss or furfural in the oil fraction and by polymerization. Another advantage is that no, or practically noJ furfural is vlost rby 'polymerization `since the. furvfural is .not subjected obtain the advantages of an excess of water over that required to give a saturated solution of furfural without the disadvantage of an excessively large amount of water. Numerous other advantages of the, presentv invention will be` apparent.

We claim:

1. The process of recoveringy furfural from admixture with foam producing oils which are not readily removed from furinral by distillation which comprises extracting such furfural-oil mixture with water at a temperature in the range from `90" to 150 Fg, controllingv the quantity of water used in the extraction so that the resulting aqueous phase is from `50 vto 25 per cent saturated with fur-rural, separately withdrawing said aqueous phase andV a resulting oil phase, subjecting said aqueous phase to fractional distillation in a fractionation column and thereby separating it into an overhead fraction of furfural and Water in azeotropic proportions and a bottoms fraction of water, condensing said overheadv and' causing the liquid condensate to separate into a water phase and a furfural`v phase essentially free `or' oils, withdrawing .said water phase and reiiuxing said, column therewith,` and separately withdrawing, said fnrfural phase as the product of the process.

2. The process of recovering furfural from admixture with foam producing oils which are not readily removed from furfural by distillation which comprises extracting such furfuraloil mixture with water at a temperature in the range from 90 to 150 F., controlling the temperature and quantity of water in the extraction so that the resulting aqueous phase does not contain more than 0.1 weight per cent of oils and the resulting oil phase does not contain more than 3 Weight per cent of furfural, separately withdrawing said aqueous phase and' oil phase, .subjecting said aqueous phase to fractional distillation in a fractionation column and thereby separating it into an overhead fraction of furfural and Water in azeotropic proportions and a bottoms fraction of water, condensing said overhead and causing the liquid condensate to separate into a water phase and a furfural phase essentially free of oils, withdrawing said Water phase and refluxing said column therewith, and separately withdrawing said furfural phase as .the product of the process.

CHARLES KEITH BUELL. CHARLES F. WEINAUG.

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

UNITED. s'rATEs eATENTs