Product Information

DuPont Terathane® Productse

Recovery of Tetrahydrofuran (THF)

ForewordReclamation of solvent from waste air or liquidstreams for reuse is often essential to the economicsuccess of an industrial process. This operation iswidely known as solvent recovery and is the subjectof this publication.

Tetrahydrofuran can be recovered safely andefficiently on an industrial scale by conventionalmethods from operations such as topcoating,printing, film casting, and chemical processes inwhich it is used as a reaction medium. It may berecovered alone or in mixtures with other solvents.

Overall recovery efficiencies at plants where THFis being recovered range from 85 to 97%. THF lossduring adsorption, drying, and separation varieswith the number of solvents involved, but seldomexceeds 3% in a properly designed and operatedrecovery system. The greatest factor influencingthe efficiency of recovery from air streams is theefficiency of vapor collection, which in turn isstrongly influenced by the degree of enclosurepermitted by the operation.

The physical properties of tetrahydrofuran that aregenerally of importance in the design of recoverysystems are listed in Table 1. Detailed informationis given on the recovery of THF from air streams,separation of THF from its water azeotrope, andseparation of THF from solvent mixtures.

Recovery of Tetrahydrofuranfrom Mixtures with AirTetrahydrofuran can be recovered safely andefficiently from lean solvent vapor-air mixtures byordinary solvent recovery procedures such asadsorption and absorption. Adsorption on activatedcarbon is the most widely used method because ofits versatility and efficiency. Absorption is seldomused but can be employed where installation ofcarbon beds is not feasible. Recovery of THF bycondensation is not generally applicable due to thehigh solvent vapor concentrations required for

Table 1Physical Properties of Tetrahydrofuran*

Boiling Point at 760 mmHg, °C (°F) 66 (151)

Specific Gravity, 20/4°C (68/39°F) 0.888

Weight, lb/gal at 20°C (68°F) 7.4

Refractive Index, n 1.4073

Latent Heat of Vaporization,cal/g, 66°C (151°F) 95

Flash Point (Tag Closed Cup), °C (°F) –20 (–4)

Flammability Limits, vol% in air,25°C (77°F), Lower 2

Upper 11.8

Miscibility: water; esters, ketones;alcohols; diethyl ether; aliphatic,aromatic, and chlorinated hydrocarbons ∞

* These properties are drawn from various DuPont and othersources. DuPont does not make any express or impliedwarranty that future production will demonstrate orcontinue to possess these typical properties.

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economical operation. Adsorption and absorptionsystems for the recovery of THF vapors are out-lined in the following section.

AdsorptionTetrahydrofuran vapor may be recovered in com-mercially available fixed-bed adsorption unitscharged with gas-adsorbent grade of activatedcarbon.1,2 The vapor-air mixture is generally drawnby a fan through a filter to remove all solid par-ticles, then cooled and blown through a bed ofactivated carbon that adsorbs the vapor and allowsthe stripped air to pass through. Typical commer-cial units provide two adsorbers connected inparallel to permit continuous solvent recovery.When one unit becomes saturated with solvent,the vapor-air flow is switched to the other adsorber.Solvent is removed from the saturated unit bypassing low pressure steam through the carbon bedcountercurrent to the direction of vapor-air flow.The steam revaporizes the solvent and carries itfrom the adsorber. A flow sheet for the recoveryof THF vapor from air by adsorption is shown inFigure 1.

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Figure 1. Recovery of Tetrahydrofuran by Carbon Adsorption

The concentration of THF vapor in exhaust airstreams from drying ovens is normally maintainedbelow 1% by volume to avoid approaching theexplosive range, 2.0 to 11.8% by volume in air.Because of this low concentration and the substan-tial volumes of vapor-air mixture resulting fromlarge-scale operations, three or more adsorbers arefrequently required. In such cases, the vapor-airmixture is passed through two adsorbers in parallelwhile the third is being steamed. Series operation isemployed when maximum recovery efficiency isdesired but requires a minimum of three and oftenfour adsorption units. To improve efficiencyfurther, adsorption systems are often equipped withautomatic sequence controls that operate on a fixedcycle or a cycle that varies to conform with solventloading. Regardless of the number of units used,they must be large enough to prevent excessive gasvelocity and provide adequate dissipation of heat ofadsorption.

Tetrahydrofuran recovery efficiencies of 98 to 99%may be expected from activated carbon adsorbers.The adsorptive capacity for THF will vary from onebrand of activated carbon to another, but 0.35 lbTHF/lb carbon is an approximate average equilib-rium value. Commercial design is often based onhalf the equilibrium value, because “breakthrough”normally occurs at about that level.

The amount of steam required for regenerationdepends on the amount of solvent in the carbon andthe physical characteristics of the carbon itself.Under normal conditions, about 3 lb steam/1 lbTHF is required, yielding a stripper still feedcontaining 25% THF. The stripper still removesgross water from the mixture, to give an azeotropicdistillate containing 5.3% water. The vapor-liquidequilibrium curve for the THF-water system atatmospheric pressure is presented in Figure 2.

It is apparent from the curve that the azeotrope maybe easily obtained in spite of wide variations in feedcomposition.

VAPOR-

LADEN AIR

FILTER

& COOLER

BLOWER

& MOTOR

VENT RETURN

ADSORBER NO. 1

ADSORBER NO. 2

CONDENSERS

EXHAUST

AIR

ACTIVATED

CARBON STRIPPER

STILL

THF-WATER

AZEOTROPE

EFFLUENT

TO WASTE

L.P.

STEAM

L.P.

STEAM

AbsorptionTetrahydrofuran may be recovered from an airstream by absorption in water where adsorption isimpractical. However, economics generally restrictconsideration of absorption to large volume recov-ery units, as the THF vapor concentration isvery low.

The absorption system depicted in Figure 3 can beused to recover THF from air streams.

In this system, the solvent vapor-air mixture isfiltered, cooled, and blown upward through acolumn where the THF is absorbed by waterflowing countercurrent to the direction of gas flow.

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Figure 2. Vapor/Liquid Equilibrium

1.0

0.8

0.6

0.4

0.2

00 0.2 0.4 0.6 0.8 1.0

Mole Fraction THF in Liquid

Mo

le F

racti

on

TH

F in

Vap

or

Vapor-Liquid EquilibriaTHF-Water760 mmHg

Figure 3. Recovery of Tetrahydrofuran by Water Absorption

VAPOR-

LADEN AIR

FILTER

& COOLER

BLOWER

& MOTOR

ABSORBER

EXHAUST

AIR

COOLER

SEWER

PREHEATER

STRIPPER

STILL

L.P. STEAM

CONDENSER

THF-WATER

AZEOTROPE

The absorber effluent is then stripped of grosswater by distillation to yield the THF-waterazeotrope. The water is recycled to the absorberto minimize solvent loss.

Separation of Tetrahydrofuranfrom Its Water AzeotropeBoth the adsorption and absorption methods ofrecovering THF yield an azeotrope containingabout 5.3% water, from which THF cannot beseparated by simple distillation. Because mostoperations require dry THF, a number of methods

for separating THF from its water azeotrope havebeen developed, and several are in commercial use.The operating principles and factors to be consid-ered in design of these systems are discussedindividually in the following sections.

Brine ExtractionTetrahydrofuran, like many other organic solvents,may be dried by extracting the water with a satu-rated calcium chloride brine solution. Figure 4illustrates the operation of this system.

The THF-water azeotrope is pumped into thebottom of the extraction column where it flowsupward, countercurrent to the saturated brinesolution. The brine removes most of the water fromthe azeotrope and flows out of the bottom of theextractor to an evaporator, where it is concentratedfor reuse. The water removed by the evaporatorcontains a small amount of THF and is recycled tothe recovery system stripper still.

The water content of the THF stream leaving thetop of the extractor is about 1.8% by weight whenproper contact between the two streams has beenmaintained. Final drying is obtained by distillingthis stream to yield dry THF and the azeotrope,which is recycled to the extractor. The watercontent of THF dried by this method can be re-duced below 0.1% when a batch still is used but ismore commonly about 0.5%, depending on theefficiency of the still.

Brine extraction is a relatively foolproof method forseparating THF from its water azeotrope and iseconomical, provided a high degree of dryness is

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Figure 4. Brine Extraction

not required. It is useful where moderate to largequantities of THF must be dried and is readilyadaptable to batch or continuous operation. Solventloss should not exceed 1% in the system described,but will be significantly larger if the recycle to thestripper still or evaporator is eliminated. The brineextraction method is particularly useful whenmixtures containing several solvents must be driedsimultaneously.

Pressure DistillationThe shift in composition of an azeotrope that occurswhen pressure is changed may be used to separateTHF from its azeotrope with water.* The waterconcentration in this azeotrope increases from 5.3%to about 12% as the pressure is increased fromatmospheric to 100 psig. This shift is showngraphically by the vapor-liquid equilibrium diagramin Figure 5.

The system shown in Figure 6 employs thisprinciple to dry THF without use of extraneouschemicals or solvents.

THF-water azeotrope from the stripper still of therecovery system is pumped under pressure througha preheater directly to the pressure still. Theoverhead stream from the pressure still is the THF-water azeotrope at 100 psig, which is recycled tothe stripper still. Dry THF containing 0.05% or less

THF-WATER

AZEOTROPE

EXTRACTION

COLUMN

BRINE

EVAPORATOR

L.P.

STEAM

L.P.

STEAM

BATCH OR

CONTINUOUS

STILL

COOLER

DRY THF

RECYCLE TO

STRIPPER STILL

CONDENSER

CONDENSER

* Can. Patent 546,591 (1957) assigned to E. I. duPont de Nemours &Co.

Figure 5. Vapor/Liquid Equilibria

1.0

0.8

0.6

0.4

0.2

00 0.2 0.4 0.6 0.8 1.0

Mole Fraction THF in Liquid

Mo

le F

racti

on

TH

F in

Vap

or

Vapor-Liquid EquilibriaTHF-Water100 psig

water is continuously removed from the base of thepressure still. While pressure distillation is capableof producing drier solvents than the other commondrying methods, the degree of dryness obtained isdetermined by design of the pressure still.

Pressure distillation is the simplest method forseparating THF from its water azeotrope and is alsothe most economical where THF is the only solvent

5

Figure 6. Pressure Distillation

RECYCLE TO

STRIPPER STILL

COOLER

COOLER

DRY THF

H.P. STEAM

CALANDRIA

CONDENSER

L.P.

STEAM

PRESSURE

STILL

THF-WATER

AZEOTROPE

to be dried, other equipment does not exist, orsubstantial quantities of THF must be dried. Thesefactors usually indicate the desirability of continu-ous operation. Multisolvent mixtures may be driedby this method, but the advantages of simplicityand economy are lost. Solvent loss should benegligible, provided all equipment is tightly sealedand the condenser-cooler combination is efficient.

Solvent ExtractionTetrahydrofuran may be effectively dried by addingcertain water-immiscible solvents to the THF-waterazeotrope.* Pentane is one of the best solvents forthis purpose because of its low price and highefficiency. A THF drying system employingpentane is illustrated in Figure 7.

The THF-water azeotrope from the stripper still iscontinuously mixed in a vessel with an equalvolume of pentane. This causes formation of twophases: an organic phase containing pentane, mostof the THF, and a small amount of water; and anaqueous phase that contains some THF and tracesof pentane. The exact composition of each phasemay be predicted from the THF-pentane-waterternary miscibility diagram shown in Figure 8.

The two-phase mixture is pumped to a decanter,where the aqueous layer is separated and recycledto the stripper still for recovery of dissolved THF.

Dry THF is obtained from the organic layer bydistilling off pentane and water. This distillation isusually carried out at a pressure of 15 psig toreduce cooling water requirements. The pentane-water condensate forms two layers, which maybe separated by decantation and recycled. THFcontaining less than 0.1% by weight water maybe recovered by this system.

With minor modifications, existing solvent recov-ery equipment may often be adapted for THFdrying by pentane extraction. However, it must berecognized that pentane is a low-boiling, low-flashsolvent that requires careful attention to equipmentdesign and safe handling procedures. The nature ofthe pentane extraction method generally restricts itsuse to continuous processing of large volumes ofTHF. Recycle of minor streams as shown shouldresult in negligible THF loss.

Other TechniquesSeveral methods that employ solids have beendeveloped for separating THF from its waterazeotrope. These are particularly useful if small tomoderate quantities of THF must be processed or ifa high degree of dryness is required. They includethe following:

• Dehydration with caustic soda• Dehydration with calcium chloride• Liquid phase adsorption

* U.S. Patent 2,790,813 (1957), Bente, P. F. (assigned to E. I. du Pontde Nemours & Company)

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Figure 7. Pentane Extraction

Caustic soda can be used effectively to dry theTHF-water azeotrope because of its strong affinityfor water. The equipment needed includes a liquid-solid contact column with the necessary tanks,pumps, and piping. The azeotrope is pumpedupward through a contact column filled with flakecaustic. Water extracted from the azeotrope by thecaustic forms a concentrated caustic solution thatflows downward and is discharged from the bottomof the column. Makeup caustic flake is added asrequired to the top of the column. The THF flowingfrom the top of the column may vary in dryness,depending on flow rate and the amount of causticused. Commercial operation has shown optimumconditions require about 4.5 lb caustic/100 lbazeotrope to yield THF containing approximately0.5% water. Under these conditions, THF lost withthe water brine is about 1% of the THF fed to thedryer. Drier solvent can be obtained where requiredby recirculation or by processing through a secondcontact column in series with the first. Traceamounts of caustic and other possible contaminantsmay be removed from the dry THF if desired bysimple distillation. This system conforms readily toeither intermittent or continuous operation.

Anhydrous calcium chloride cannot be used di-rectly to dry the THF-water azeotrope, because itreacts with THF to form a solid white complex oretherate. Formation of the etherate is accompaniedby considerable evolution of heat and expansion involume, which may cause plugging if THF is fed

directly into a column of calcium chloride. How-ever, the etherate itself shows an affinity for waterand is suitable for drying the azeotrope.*

Equipment for drying with calcium chlorideetherate is similar to that for drying with causticsoda. The initial charge of etherate may be preparedby slurrying anhydrous calcium chloride into THFin the contacting column. After the column ischarged with etherate, the THF-water azeotrope ispumped upwards through the column, where thewater is removed by the etherate (forming a sepa-rate liquid phase of concentrated brine containingsome THF). Dry THF flows from the top of thecolumn and the brine layer is discharged from thebottom. Calcium chloride makeup may be chargedas required directly into the top of the columnwithout danger of plugging. Based on laboratorydata, operation to produce THF dried to 0.5% waterrequires about 3 lb calcium chloride/100 lb azeo-trope. At this brine concentration, approximately0.6% of the THF fed to the dryer will be lost in thewaste brine stream.

Liquid-phase adsorption is the method commonlyused to obtain very dry solvent when the quantity ofTHF-water azeotrope does not justify investment inpressure distillation equipment. Type 4A molecularsieves3,4,5 have proved to be particularly usefuladsorbents for water in THF because of their high

* U.S. Patent 2,795,591 (1957), Bente, P. F. (assigned to E. I. du Pontde Nemours & Company)

COOLER

DRY THF

CONDENSER

DECANTER

DECANTER

CALANDRIA

RECYCLE TO

STRIPPER STILL

L.P.

STEAM

CONTINUOUS

STILL

THF-WATER

AZEOTROPE

MIX

TANK

7

THF

SINGLEPHASE

9

8

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1TWO

PHASE

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7

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9PENTANE WATER

Figure 8. Ternary Miscibility—THF, Pentane, Water at 25°C (77°F), wt%

adsorption capacity at low water concentrations.Pilot scale tests have indicated that adsorptivecapacity may vary from 5 to 12 lb water/100 lbadsorbent, depending on the degree of drynessrequired. Efficient operation can reduce the watercontent of THF to a value of 0.002%.

Azeotrope to be dried by liquid phase adsorption isusually semi-dried to a water content of 0.5 to 1.0%by one of the techniques previously described tominimize adsorbent investment and regenerationcost. The semi-dried THF is then pumped upwardthrough a column filled with adsorbent to achievefinal drying. Any of several commercially availableadsorption units may be used.6 When the adsorberceases to provide the dryness required, operation isterminated or switched to a parallel unit to permitregeneration of the saturated adsorbent. Regenera-tion of the adsorbent is accomplished by drainingall liquid from the adsorbent bed, heating it toabout 400°C (752°F), and cooling to ready it for

reuse. Heat for regeneration may be derived fromelectricity, steam, or gas. Plant scale installationsfrequently contain parallel adsorbers controlled byan automatic cycle timer to provide uninterruptedservice.

Separation of Tetrahydrofuranfrom Solvent MixturesTetrahydrofuran is often used in combination withother organic solvents to increase solvent power orcontribute other valuable properties. Althoughseparation of solvents is generally more complexthan drying a one-component system, solventseparation is usually practical and may often bedone in existing equipment. Factors that must beconsidered when selecting the separation methodare the physical nature of the mixture and theazeotropic combinations that may be present. Forexample, the mixture may be in one or two liquidphases and may contain suspended or dissolved

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solids. In addition, azeotropic combinationsbetween solvents occur frequently. The knownbinary azeotropes of THF are listed in Table 2.

Separation of THF from specific solvent mixturesmay involve one or more addition, decantation, ordistillation steps, depending on the identity andnumber of solvents. DuPont welcomes the opportu-nity to make suggestions on the most efficient,economical system for recovery of THF fromparticular solvent mixtures. This assistance maybe obtained by contacting our Customer ServiceCenter.

Several solvent mixtures containing THF areencountered frequently in industrial operations.These mixtures include the ternary systems THF-toluene-water and THF-methyl ethyl ketone-water.Important factors in the design and operation ofprocesses for the separation of these mixtures arediscussed in the following sections.

Reaction solvent mixtures containing THF arefrequently used in the chemical and allied indus-tries. A simple new technique for recovering boththe reaction product and THF in high yields is alsodiscussed.

Tetrahydrofuran-Toluene-WaterToluene is used as a diluent for THF in coatingoperations and is recovered concurrently. Conden-sate from the activated carbon adsorber containsTHF, toluene, and water in two ill-defined liquidphases. A system that efficiently separates and driesboth THF and toluene is shown schematically inFigure 9.

Condensate from the adsorber is collected in a mixtank together with several recycle streams. Addi-tional toluene is added, if necessary, to effectadequate phase separation and to extract theoptimum amount of THF into the organic phase.The content of the mix tank is then pumped to adecanter where the layers separate. The exactcomposition of each layer may be predicted fromthe THF-toluene-water ternary miscibility diagramshown in Figure 10, if the overall composition isknown.

The aqueous layer containing dissolved THF and alittle toluene is distilled to recover residual solventthat is recycled to the mix tank for extraction. Theorganic layer consisting of toluene, most of theTHF, and a small quantity of dissolved water ischarged to a batch still for separation. The first cutremoves all water in the form of THF-water azeo-trope that is recycled to the mix tank for extraction.The second cut is essentially pure, water-free THF.The water content of the THF varies, depending onthe still efficiency and the care with which the cutis made; however, average conditions should yieldTHF containing less than 0.3% water. On completeremoval of THF, the distillation is terminated andthe toluene withdrawn from the boiler and cooledfor reuse. Distillation of the organic layer may beadapted for continuous operation, provided thevolume involved justifies the additional investment.

Tetrahydrofuran-Methyl EthylKetone-WaterTetrahydrofuran is frequently used with methylethyl ketone (MEK) in topcoating and other resinsolutions to increase solids content and drying ratewithout increasing viscosity. Solvent vapor recov-ery results in a mixture of THF, MEK, and water,which is usually a single liquid phase. The miscibil-ity characteristics of this ternary system at 25°C(77°F) are shown in Figure 11.

In some cases, THF and MEK are present in theratio desired for reuse. Under these circumstances,the solvent mixture may be dried by distilling offthe water azeotrope of each mixture with brine orcaustic soda, depending on the dryness required.

In most cases, it is necessary both to dry andseparate the solvents prior to reuse. These opera-tions may generally be carried out in existingrecovery systems after minor modification.

A typical solvent recovery system that has beenmodified to separate MEK and THF might operatein the following manner. Condensate from theactivated carbon adsorber is stripped of excess

Table 2Binary Azeotropes of Tetrahydrofuran

Component A: Tetrahydrofuran; b.p., 66°C (150°F)

Component B b.p. B, °C (°F) b.p. Azeotrope, °C (°F) wt% B

Chloroform 61.2 (141) 72.5 (161) 65.5Cis-dichloroethylene 60.3 (140) 69.9 (157) 46.0Ethanol 78.4 (172) — 10.0n-Hexane 68.9 (154) 63.0 (145) 53.5Methanol 64.7 (147) 60.7 (140) 31.0Water 100.0 (212) 64.0 (147) 5.3

9

Figure 9. Toulene Extraction

water by distillation to yield the water azeotrope ofeach solvent. The combined azeotropes are fedupward through an extraction column packed withcalcium chloride etherate to reduce the overallwater concentration to about 0.5%. This mixture ischarged to a batch still for separation. The first cut,THF-water azeotrope, is recycled to the extractioncolumn for drying. The second cut is essentiallypure, dry THF. Upon complete removal of THF, thedistillation is terminated, and the dry MEK remain-ing in the still boiler is cooled for reuse. Based ontheoretical considerations, this system is capable ofdrying solvents to less than 0.1% water. In com-mercial practice, water contents up to 0.5% may beexpected.

Reaction Solvent MixturesTetrahydrofuran’s unique solvent power and itsability to direct reactions are leading to wideacceptance by industry as a solvent for Grignardreactions and lithium aluminum hydride reductions.The principal consideration in the use of THF inthese applications is its complete water miscibility.This complicates recovery of dry solvent from thereaction mixture.

One simple method for recovering both THF andproduct in high yield is by addition of a waterimmiscible co-solvent to reaction mixturescontaining THF, water, and the organic productbefore decanting the organic layer. Pentane, tolu-ene, and xylene are all suitable for this purpose. Onaddition of the co-solvent, the water content of theorganic layer and the THF content of water layerboth decrease sharply. The concentration of thereaction product dissolved in the water layer is alsolowered significantly.

THF suitable for reuse is recovered from theorganic layer decantation by conventional dryingand distillation. Molecular sieves3,4,5 have provedspecially useful for drying organic liquid mixtures.

Safety ConsiderationsLike most organic solvents, tetrahydrofuran is avolatile, flammable liquid that may be hazardous tohealth if it is improperly handled. These propertiessuggest that certain precautions be considered in thedesign and operation of recovery systems.

CONDENSATE

FROM ADSORBER

MIX

TANKDECANTER

CONDENSER

COOLER

TOLUENE TO STORAGE

CONDENSER

DRY THF

L.P.

STEAM

L.P.

STEAM

BATCH OR

CONTINUOUS

STILL

STRIPPER

STILL

EFFLUENT

TO WASTE

10

THF

SINGLEPHASE

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3

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1TWO

PHASE

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1

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9

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9

TOLUENE WATER

6

8

8

Figure 10. Ternary Miscibility—THF, Toluene, Water at 25°C (77°F), wt%

The flash point of THF measured by Tag closedcup is –20°C (–4°F), and its boiling point is 66°C(151°F). This places it in the same fire hazardgroup as acetone, VM&P naphtha, methyl ethylketone, and a number of other commonly usedsolvents that ignite at room temperature. Theprecautions normally used to prevent fires whenhandling such solvents should be used whenrecovering THF. THF vapor forms explosivemixtures with air between the limits of 2.0% and11.8% by volume at room temperature. At 100°C(212°F), the limits become 2.1% and 12.0% byvolume. The THF vapor concentration in exhaustair from drying ovens should always be maintainedwell below the lower explosive limits; 50% of thelower explosive limit is a commonly acceptedmaximum operating level.

The generally accepted threshold limit value forTHF is 200 parts per million parts of air. It isunlikely that excessive exposure to THF vapor will

occur during normal operation of properly designedsolvent vapor recovery equipment, because properdesign usually results in average concentrationswell below 100 ppm in the immediate vicinity ofcoating, printing, or film casting machines. Exces-sive exposure to THF vapor is also unlikely,because the odor is detectable by most people atconcentrations of 25 to 50 ppm, a level well belowthe threshold limit.*

The third factor that must be considered forsafe design of THF recovery systems is the possiblepresence of tetrahydrofuran hydroperoxide(THF-peroxide). This material forms in THFexposed to air and can decompose violently when itbecomes sufficiently concentrated. A general rulefor organic peroxides is that they may be easilyhandled in concentrations below 5% by weight.

* Due to some recent studies, DuPont has revised its AEL limits to25 ppm and its STEL limits to 75 ppm.

11

Figure 11. Ternary Miscibility—THF, MEK, Water at 25°C (77°F), wt%

Applied to THF-peroxide, this rule indicates that itsconcentration in THF should not be permitted toexceed 5%, if distillation is contemplated. Caremust always be exercised when distilling THFalone or in mixtures to avoid distilling to dryness,particularly in distillations associated with recov-ery. Distilling to dryness may concentrate the smallquantity of THF peroxide normally present in thesolvent or its solutions and increases the possibilityof violent decomposition.

DuPont THF is stabilized with butylated hydroxy-toluene (BHT) to prevent formation and/or accumu-lation of THF-peroxide during storage. However,the stabilizer is a relatively high boiling compoundand is left behind when THF is evaporated. Conse-quently, the THF vapor exhausted from a dryingoven is unstabilized and may form a small quantityof THF-peroxide that is adsorbed and decomposedin the activated carbon during recovery operations.Laboratory studies have shown that ordinary

solvent recovery grades of activated carbon,1,2

which contain between 15 ppm and 75 ppm of ironas a natural impurity, decompose THF-peroxideand help prevent its formation.* Industrial experi-ence has confirmed these findings.

Although it is apparent from the above discussionthat hazardous amounts of THF-peroxide shouldnot accumulate in recovery systems, periodicchecks should be made for possible peroxidecontent. If recovered THF is to be stored for anextended period, it should be restabilized orblanketed with an inert gas atmosphere. For moredetails on the properties, uses, storage, and han-dling of THF, please refer to the DuPont THFPUSH bulletin available upon request through ourCustomer Service Center.

* U.S. Patent 2,790,813 (1957) Bente , P. F. (assigned to E. I. du Pontde Nemours & Company)

THF

SINGLEPHASE

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PHASE

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9MEK WATER

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(7/00) W-400446 Printed in U.S.A.Reorder No.: H-88074 DuPont Terathane® Products

e

Contact us on the web: http://www.dupont.com/terathane

The information set forth herein is furnished free of charge and is based on technical data that DuPont believes to be reliable. It is intended for use bypersons having technical skill and at their own discretion and risk. Because conditions of use are outside of our control, we make no warranties, expressor implied, and assume no liability in connection with any use of this information. Nothing herein is to be taken as a license to operate under or arecommendation to infringe any patents.

EquipmentTetrahydrofuran may be handled in ordinary steel,because it is noncorrosive and does not hydrolyze.Mixtures of THF with other solvents or chemicalsmay require a material more resistant than steel.Specific recommendations can be offered onlywhen the system is known.

Activated carbon adsorption equipment suitable forTHF recovery is available from several manufactur-ers.7,8 Other equipment required for the variousTHF recovery systems such as stills, heat exchang-ers, extractors, and tanks is available in standardmodels or on a custom-made basis from a numberof process equipment fabricators. Reference tothese firms may be found in the Thomas’ Registerof American Manufacturers, Sweet’s Catalog File,and similar compilations.

Some equipment fabricators7,8 are able to designand construct complete solvent recovery systemsincluding adsorbers and all separation equipment.Where recovery equipment does not now exist, thisapproach offers the advantage of a completelyintegrated recovery system.

Source of MaterialsThe DuPont Company does not imply by citationof these manufacturers that only their products willperform satisfactorily. The products of othermanufacturers that are not listed may be equallyor better suited for the purpose.

Activated Carbon1 Barneby-Sutcliffe

A Division of WaterlinkP.O. Box 2526Columbus, Ohio 43216Web Site: http://www.bscarbons.com/

2 Calgon Carbon Corp.P.O. Box 1346Pittsburgh, Pennsylvania 15230Web Site: http://www.calgoncarbon.com/

Adsorbents and Resins3Grace DavisonW. R. Grace Co.7500 Grace DriveColumbia, MarylandWeb Site: http://www.gracedavison.com/

4Rohm and Haas Co.5000 Richmond St.Philadelphia, Pennsylvania 19137Web Site: http://www.rohmhaas.com/

5Union Carbide Corporation39 Old Ridgeway RoadDanbury, Connecticut 06817Web Site: http://www.unioncarbide.com/

Liquid Phase Adsorption Units6Lectrodryer DivisionAjax Magnethermic Corp.230 Geri LaneRichmond, Kentucky 40475Web Site: http://www.lectrodryer.com/

Solvent Recovery Equipment7 Koch-Glitsch, Inc.

4111 E. 37th Street NorthWichita, Kansas 67220Web Site: http://www.koch-glitsch.com/

8 Barneby-SutcliffeA Division of WaterlinkP.O. Box 2526Columbus, Ohio 43216Web Site: http://www.bscarbons.com/

For additional information or to place an order:

Americas 800-441-3893 fax 302-992-2500Europe 49-6172-871306 fax 49-6172-871306Australia 61-2-9923-6111 fax 61-2-9923-6099P.R. China 86-21-6386-6366 fax 86-21-6386-6333

Japan 81-3-5434-6124 fax 81-3-5434-6189Korea 82-2-222-5306 fax 82-2-222-5319Taiwan 886-2-514-4419 fax 886-2-514-4364Other Asia 82-2-222-5306 fax 82-2-222-5319