Laboratory Steam Distillation Using Electrically Generated Superheated Steam R. K. Lane.l M. W. Adkins. and E. J. Eisenbraun2 ~,P. D. ~rovence.~ Oklahoma State University, Stillwater. OK 74078 ~~~~~~
The use and advantaees of superheated steam for laboratory steam distillatim and the design of an effective flameheated eenerator for superheated steam have been described by ~ e w m a n(I). The &safety codes in our laboratories prohibit use of open flames if other laboratory operations, involving flammable materials, are in progress. T o overcome this limitation, we developed the electrically heated apparatus shown in the fienre. Safety Considerations. Since uninsulated electrical connections are used in oneratine the apparatus and hieh temperatures are attained, all pe&onn;fshould be thoroughly trained. Unsupervised initial use should not be permitted and constant attendance during use, is mandatory. We have found carefully worded, stepwise, typewritten instructions to be essential. These instructions should include statements of what to expect and how to react t o equipment failure. Safety glasses are t o be worn a t all t i m i s a n d a face shield and/or plastic equipment shield i s advisable. Insulated gloves a r e needed to handle hot glassware. Apparatus Design. While sufficient detail is provided in the figure to enable duplication of the apparatus, some comments on design, as it affects operation and safety requirements. are needed. The parts of the apparatus are numbered and lettered to follow tbk flowof steamfrom itsgeneration in the flask at point 2 to condensation a t point 13a. Deionized water should be used in the steam generator to avoid corrosion of metal Darts and electrolvsis of water. Accumulation salts increaseconduction of cuirent, leading to power failures. Variacs (110 V, ac, 10 amp) were used a t la-le to provide control of electrical variation and load distribution to reduce the possibility of overloading an individual Variac. All of these Variacs are wall mounted as a precaution against water spills. Starting from room temperature with a full generating flask 2, steam may be produced in 10-20 min using 100-110 V ac. During operation, 90-110 V are used. If there is a power failure or the Variac settine of l c to heater 3f is reduced suddenly, material is siphoned from the swam pot 9 to the trap 4s. or the eeneratine flask 2. The steam condensate trap a s s k m b ~4aSc, ~, is needed to collect line condensate and to provide a rapidlv openable outlet should there he need to i e n t excess sieam p;essure or to prevent backup of material as mentioned above. The superheater assembly consists of dual-wall quartz tubing, 6a and 6b, wrapped with two 230-cm lengths of Nichrome ribbon heaters rated at 0.09 nlcm. These heaters are insulated with a wrapping of ceramic fiber tape3which in turn is covered with Pyrex glass tape. Cutout, 6c, is shown to provide a view of the Nichrome ribbons. To distribute the electrical load. the Nichrome heater was divided into two sections ( ~ a r i i c lsa and lb). To minimize splashing from the steam pot 9 to the condenser 13a, the still head 12, 35 mm 0.d. tubing, was fitted ~~~~
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' Undergraduate research asslsmt.3.
Corresponding author. Sargent Welch. Catalog 133. Part No. S-1210-10D.
with square glass baffles. A spherical 50130 joint, 5f, was selected for the steam pot 9 to provide an adequate opening for return of materiai to it, ih the event of-foaming and bumping. Magnetic stirring also is helpful to minimize humping. However, if temperatures in excess of 250 "C are planned for the steam pot, the Teflon-covered magnetic stirrinz should be~ omitted since some maenetism is lost . ~ -har -~-~~ and the Teflon coating degrades (2). An inexpensive magnetic stirrer of local construction. has been described (3). The heating mantle 11 is included to prevent accumulation of water durine conventional steam distillation and to help maintain a dry steam pot during superheated steam distillation.A Variac setting of 45-60 V is usually adequate. Aluminum foil or heat resistant fabric may be used to insulate the steam pot 9 and the still head 12. The still head 12 is vacuum jacketed which also reduces thermal loss. I t should be noted that superheated steam distillation does not begin untilallcondensed water is evaporated from the steam pot 9. Durine steam distillation of solid or high molecular weight compounds, the condenser 13a-c may become obstructed (another reason for including quick opening clamp 4c). T o reduce this possibility, we useahultichannd condenser (see cross section 13b). This design also provides an increased condensing capacity. The condenser should terminate with a 35/20 ball for attachment of tip 13c. A multitube condenser, usine stainless steel tubes. which has *proven ideal for this appccation has been described (4). In the event that condenser, 13a, contains desired solid product, it may he detached and a round-hottomed flask containine- appropriate refluxine solvent and a magnetic .. stirring bar and fitted with a heaiing mantle is connected to the bottom of condenser 13a to dissolve material from the interior of the condenser. During this operation, water is drained from the condenser. If necessary, a second condenser may he added to the top of condenser 13a to retain the refluxing solvent. Spherical joints are used a t all points except in the steam generating flask 2. This type of joint is superior since it allows some flexing, rarely freezes, and can be securely clamped to prevent loss of material and steam leaks. The snherical ioints at 5a and 5c are auartz 35/20 and 28/15. rkspectiveiy. All other joints are Pyrex. Standard taper joints areused in the steam generator flask to provide apoint at which a stopper can blow out if excessive pressure develops. The operator should make certain these joints are not f k e n before steam is generated and they should not be clamped at any time. For compounds melting below the bp of water, solids may be allowed to accumulate in the condenser. The condenser is drained as needed to melt the comnound and allow it to drain into a receiver. In some cases, it is preferable to drain the cooling water from the condenser and k e e ~ the tin of the condenser submerged in water or ice water to condense the steam and oroduct. This latter techniaue is useful for hieh meltingcompounds, e.g., adipic acid. However, c a r e must be taken to avoid drawing water back t o t h e steam . pot ~ .a r t i c u larly during useof superheated steam. This can result in a violent vaporization of water and the resulting tempera-
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April 1987
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Superheated steam distillation apparatus
1. a-e. Variac. Mcdel WlOMT3. 2. Steam generator flask. 5-L. 45/50 and 24/40. 3. Electrical heater assembly: a. Alligatw clip. sheathed with Y ni., silicon rubber tubing. b. Teflon adapter. 10/20. Ace Glass Co.. Vineland. NJ 83060. Cat. #8299-10. C. Adapter, glass, 24/40 to 10130, Ace Glass Co., Cat. #5021-09. d. Capper conductor, ' I ,in. X 8 in.. threaded at each end and flned wHh two brass nuts at lower end. e. Capper wire, son. 1.5 mm. I.Heating element, HAS-Ol8K from Heat Gun 201. 12 amp: Master An~liance Corn. Racine. WI 53403. , 4. Steam condensate nap assembly: a. Glass trap. 45/50 Inner joint. 35/20 Pyrex socket (5b). b. Silicon rubber tubing c. Clamp. tubing. Ace Glass Co.. Cat. #11140-02. 5. Ball and socket joints: a. Quartz ball, 35/20. b. Pyrex socket. 35/20. C. Quar1z ball, 28/15. d Pvrex socket. 28/15. e Pyrex oall and socket. 35120 f Pyrex ball and socket. 50130 6. Superheated steam generator assembly: a. Ouanr tube, double wall, fined with 35/20 quanz ball at banom and
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8. 9. 10. 11. 12. ~
13.
28/35 quartz ball at side. Overall lengm 50 cm. b. Insulation covering. 6b, consists of ceramic fiber !ape wvered wilh several layers at Pyrex tape. See fodnote 3. C. Nichrome heatina ribban s ~ l r awrmoed l .. around 6a. 2 rnm wide X 230 cm long rated a t i 09 n& 2 each Temperatwe measurement assembly a-c Wells lor Tnermocoup s l~ran/ConsIanlan) d. Digital lhermameter, not shown. Steam inlet tube. 28/15 sacket and 35/20 ball extended wllh 18 mm 0.d. tubing at lhe lower end. Steam Pat. 50130 socket. fined with msrmocouple well. 500 mL and larger. Teflon coated maonetic stinins bar w e d below 250 OC. Sea rstsrenw 2. Heating mantle to fi 9. Ace Glass Co.. Cat. X12035. Still head, glass, vacuum jacketed, fined wnh thermocouple well 70 and squam Spray bafflesas shown. a. Condenser, water 35/20 socket. 5 parallel 10 mm 0.d. X 25 a Condensationtubes. b. Cross section of 13a. C . Condenser extension tip. 35/20 socket. Mametic stirrer. " Laboratory jack. Wocden stand. Cork ring. ~~
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14. 15. 16. 17. 18. Receiver.
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Superheated Steam Dlstillatlon
Cwnpound
Temperature m~ 'C g Conden7a 7b 7c Sample sate
g Pmd uct
ACIDS Adipie acid 235 C~H~OI Myristic acid 100 + C W H ~ ~ C O ~ H236 Stearic acid 229 RCIIHZICOZH ALCOHOLS I-Octadecand 239 ffilsHaO ESTERS Triacetin 480 CsH,,Os Methyl abietate 100 '3bA 347 HYDROCARBONS Eieosane 100 IFC20H12 236 Docosane 224
rnplbp
'c 1541265= 551250~ 69/361
601210°
-781260 365
381343
Valise m i n g 01 95 V lor la and 80 V fa i b , lc and l d were wed 'Condenser easW c W , bee dlscus~M. "At 100 mm. *95 V for IC and 45 V for lbsuperheater not "red. *At 15 mm. '95vfor lcand 1 0 O V f a l a s M ib. * A ma film was k r v e d on the condensate.
ture change also may crack the steam pot. We have experienced this problem, and vigilance is needed to avoid accidents. As shown in the figure, jacks are used as supports. These are essential to manipulate the hot flasks safely. An inexpensive jack of local construction has been described (5).
To determine whether the design shown in the figure is suitable. we selected several test exneriments to show: (1) . . the temperature at several points in the apparatus using a variety of Variac settings, (2) comparison of the quantity of steam condensed and the quantity of product made using superheated steam and conventional steam. The temperature a t various points in the apparatus was monitored with ironlconstantan thermocouples to determine the most appropriate Variac settings for generation of superheated steam and maintenance of the apparatus temperatwe during a run. T o gain experience, th&eam generator was operated at 90-110 V. The condensate measured 203 4 m l l k i n , respectively. Using these Variac settings, temperature readings varying from 200-595 'C, 135-385 O C , and 112-270 "C for la. 7b. and I c were obtained. Durina routine distillations, a setting 01 9 5 \' for Variac l c u,as used while suwrheater Variacq la and it, were chanaed as nerded 10 achieve steam distillation in a reasonable time. We selected from readily available f a t t y acids, dicarboxylic acids, n-alkanes, alcohols, and esters for the studs. These results are presented in the table. ~enerationsof students have been taught in organic chemistry laboratories that dicarboxylic acids do not steam distill (6). Therefore, we could not resist including adipic acid in this study. As reported in the table, superheated steam distillation readily takes place at 1 5 9 'C. The other data in the table also provide guidance about the effectiveness of superheated steam distillation. Literature Cited 1. Newrnan,M.S. An Aduaneed Or~onicLaboroloryCoursz; Maernillan: New York. 1972. p 156. 2. M w c k Index. 9th od., Merek: Rahway. NJ, 1976. p 985, cntri7361. 3. Hai1.H.; Eisenbraun,E. J. J.Chem.Edue. 1977,54,229. 4. Lane, R. K.;Adkins, M W.;Hsil, H.: Eisenbraun, E.J. J Chem. Edwc 1986.83.985. 6. Ha1i.H.;Eisnhraun,E. J. J . ChemEduc. 1978,55,606. 6. Shiiner,R. L.: Fuson, R. C.; C~rt8in.D.Y.; M0rriI.T. C. TheSysl~molieIdenll/icofidn of Organic Compounds, 6th ad.; Wdey: New York, 1980,p 369.
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Number 4
April 1967
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