US 2608528 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
l1g- 25, 1952 J. J. PlRos ETAL 2,608,523
MICROSTILL Filed March 11, 1949 v 2 SHEETS-f-SHEET 1 INVENTO RS JI? @Zins Piras Jfnerf Glane/- l B ATTO RN EYS JQ J. PIROS El' AL Aug. Z6, 1952 MICROSTILL 2 SHEETS-SHEET 2 Filed March 11, 1949 TTORN EYS FlG. 3
Patented Aug. 26, 1952 UNITED STATES PATENr 'c') 41-"1=1lcE-5A .lohn J. Piros, Homewood, Ill., and `lohn A. Glover, Munster, Ind., assignors, by mesne assignments, to Sinclair Research Laboratories, Inc., Harvey, Ill., a corporation of Delaware Application March 11, 1949, seria; No. 80,796
This invention relates to an improved laboratory micro-still suitable for use in the precision fractionation of small volumes of mixtures of liquids having different boiling points.
Laboratory micro-stills for use in the analysis of small volumes of mixtures of liquids having dif ferent boiling points are known in the art, being described, for example, in Svensk Kem. Tids. 58, 145-150 (1946). Such stills, in. addition to comprising a still pot for holding the charge, iractionating tube Yandcondenser system, also comprise a rotatable element disposed within the fractionating tube to` aid in the fractionationl While such stills are useful for their intended purpose, there is a need in the art for a: laboratory micro-Still of improved `fractionating efficiency. Itis the object of the present invention to supply that need. i The conventional stills of the .type `described have as their rotatable element a metallic band, and the object of the present invention is accomplished `by replacing such metallic band by a flattened helical wire coil, preferably wound upon a metallic band toprovide support for such coil. The iiattened helical wire` coil has transverse major and minor axes ata right angle to its longitudinal axis, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major axis being less than the diameter of said fractionating tube. Y When such a coil is employed, it is believed that the improved fractionating efficiency is obtained by increasing the wetted Wall effect upon the sides of the fractionating tube by producing point contacting or wall ridges, instead of the window wiping effect produced by the spinning band of a conventional micro-still. i
A specic and preferred formof micro-still constructed in accordance with the present invention comprises a relatively long, thin, glass, fractionating tube which is provided near its upper end with two condensers, one spaced above the other. The lower condenser is adapted to receive cooling uidthrough the control of the flow of which the extent of the condensation effected in this primary condenser is regulated. The second condenser, located above the primary condenser, is al total or final condenser and is adapted to condense all of the vapor passing the iirst condenser and to deliver` such condensedyapor into atake- 9 claims. (o1. 2oz- 158) 4 n off` line.
The fractionating tube, from a short distance above its lower end which is connected to a still pot. up to slightly below the bottom of the primary condenser section, is provided with 1 a flattened helical wire coil. This element is slightly smaller in ,diameter than )the internal diameter of the fractionating tube Vand is connected at its upper end to a rotatable shaft which extends through the remainder of the fractionating:` tube, including the two condensing sections thereof, emerges from the upper end of the second condenser, and is connected to a variable speed electric motor.` Rotation of this element produces a ,wetted wall effect within the iractionating tube, thus producing intimate contact between the up-rising vapors and the returning reflux'on the column wall. Accurately` controllable heating means are `provided for supplying heat to the still pot, and the still pot and heating element assembly are enclosed within a vacuumv flask which is removably seated at its upper end` against the bottom of a second vacuum flask which substantially encloses the fractionating tube, both condensers, and the take-off line. To minimize radiated heat losses, this latter vacuum jacket is insulated up to the total Ycondensing section,v and heat is supplied to the jacket to compensate for heat lost therethrough, thus assuring adiabatic operation of the still..
By regulating the flow of cooling fluid through the primary condenser, the total boil-up within thefractionating tube may be condensed and returned as reflux through the fractionating tube. Also, by lproper regulation of the cooling fluid flowing through the primary condenser, which may be determined by the indication oi thermocouples located just below Aand just above the primary condensing chamber adjacent the fractionating tube, a portion of the boil-up vapors may be allowed to pass through the primary condenser, to be condensed by the final condenser from which the condensate is delivered to the take-nii line. In this manner the reux ratio may be accurately controlled and regulated to any desired value. This arrangement additionally provides for automatic indication of the end of the fractionation of one component,rsince the take-off rate decreases and the reux. ratio increases as the fractionation of one component approaches the endpoint. Also, the primary condenser must heat up to the-vaporization tempera- 3 ture of the succeeding component before additional vapor will pass through the primary condenser. Y
These features and advantages are made more apparent by the following detailed description, taken in conjunction with the accompanying drawings, in which:
Fig. 1 shows one embodiment of a micro-still in vertical section according to this invention;
Figs. 2 and 3 show another embodiment of a micro-still according to this invention;
Fig. 2 vbeing thelupper verticalsectio'n and "Fig, 3 being tlielowervertical section;
Fig. 4 is an enlarged front view of the unsup ported helical wire coil employed in the still shown in Fig. 1; l
Fig. 5 is a side view of the coil shown in Fig. 4;
Fig. 6 is an enlarged front viewof the supported helical wire coil employed in the still shown in Figs. 2 and 3; and
Fig. 7 is a side view of the coil shown in Fig'. 6.
In the micro-still of Fig. l, the fractionatng.
column consists of a thin glass tube I, having an internal diameter, e. g. of about 3 mm., more or less, and an active fractionating length, e. g. of 'around 40 cm. The upper portion of the tube is*equippedwith two condensers, a primary or partial condenser 2 and a final ortotal condenser 3. The primary condenser is formed integrally with'the fractionating `tube and its internal crosssection'area is largerthan the fractionating tube tov provide space for afthermowell il. A chamber Ia, whichextends `from the .fractionating tube I and' closed atfits. upper end, surrounds the thermowell d-'adjacent the primary condenser so thatithe thermocouples for measuring the' temperature within thiscondenser are-exposed indirectlyfon'all' sides to the vapor. VThe portion of the thermowell adjacent the primary condenser` is-adalptedto 4accommodate two thermocouples 5 andY-'Sfor indicating respectively the vapor temperaturejustbelow-and just above this condenser. Suitable connections? and 8 are provided for supplyingcooling fluid tothe condenser. The'fractionating tube extends above the primarycondenser and terminates around the total condenser `3 -which-is Aillustrated as a cold finger typeicondenser. Thiscondenser is provided with entranceand exitconnectors I0 and II for supplying cooling fluid thereto. The lowerwall 'portions off'condenser 3 are formed and sloped to drain all vapor condensing thereon onto a dripper i2 which is formed integrally with the condenser. The dripperis arranged to drip condensate therefrom-:into'a take-oif line I4, formed integrally withthe fractionating tube. Y Apear-shaped Ystill pot I5 having a capacity, eegof` about l0 c'c., and provided with a thermowell"- I1 is removably connected to the bottom of the fractionating column, and heat is supplied theretoby-a radiant heater IB. '-*Th'eheater consists of a glass form I9 within which a lNichrome wire heating coil 20 is sup` ported. A voltage regulator (not Shown) is used to--control a fluctuating input voltage to give a constant 115 volts output, anda reducing transformer (not shown), connected to the output of the voltage regulator, supplies a voltage of about 30 volts'to the heating coil. Heater I8 is resiliently supported against the bottom of pot I6 by a spring 22 which surrounds a projection 23 of form I9, and the lower end of the spring rests on the vacuum jacket 24 which mayVAI be internallysilvered and which encloses the entire still pot and heater assembly. A transit 4 disk 25 disposed within the vacuum jacket assists in positioning the spring therein. A strip of the jacket may be left unsilvered to permit the still pot and the end of the fractionating tube to be observed.
In place of stationary packing employed in fractionating columns, the column of this improved micro-still is provided with a flattened helical coil 2S, made of two No. 32 Nichrome wires wound at single wire width spacing to give a flattened double wire coil one mm. thick and of slightly less diameter than the internal diameter of the fractionating tube. For example, if the internal diameter of the fractionating tube is 2.75 mm., the diameter of the helical coil may be 2.7 mm. When larger diameter tubes are employed the diameter of the coil may be increased accordingly, if f desired. Coil 26 extends through the tube I for a length of approximately 40 cm. from a short distance above 'the still pot I6 to just below the lower end of the primary condenser section. The upper end of the coil is connected, e. g., silver soldered, to a length of thin tungsten rod 27. This rod passes through the upper sections of the fractionating tube, includingV the condensing sections, and through an opening 9 formed in the total condenser as a restricted extension of the fractionating column. Complete condensation of vapors entering this restricted opening is assured by virtue ofthe condensing surfaces provided on the total condenser adjacent such opening.
The upper end of rod 2l is adapted to be connected to the chuck of a variable speed electric motor. vRotationof coil 26 through rod'21 pro-V duces a wetted wall effect Within the fractionating tube, thereby providing high fractionating efficiency in the small Ysize columns described. The enlargement I3 of the restricted opening 9 in condenser 3 provides for now of the condensate, which is formed within the restricted opening, down along the sides of the condenser rather than down the shaft 27, thereby minimizing the return to the still pot of vapors condensed within restricted opening 9.
The fractionating tube, the entire partial condenser, the chamber within which most of the total condenser is positioned, and the takeoff line are enclosed within an integral vacuum jacket 39 1 which may be silvered internally up to the total condensing zone to minimize radiated heat losses. The `channel for thermowell 4 extends through the wall of jacket 30 near the upper end thereof. v
In order vto assure adiabatic fractionation conditions throughout the column and in order to provide for the same linear expansion in the jacket as in the fractionating tube, jacket 38 is insulated and heat is supplied thereto. To this end an exploring thermowell 3| is positioned adjacent the surface of the jacket and the thermowell and jacket are wrapped together in a layer ofglass cloth tape 32. A suitable length, e. g., about 20 feet, of Nichrome heating ribbon 33 is uniformly wound over the tape and a layer of glass wool 34 about 1/ inch in thickness is wrappedover `the ribbon. The entire assembly is then wound'with an external layer of glass cloth tape 35. The terminals 0f the Nichrome ribbon may be connected to a normal voltage source such as about volts through a reducing and regulating transformer.V
Any suitable receiver may be employed for collecting the condensate from the take-oli line. In the still illustrated, a graduated pipette 38 is removably connected to the portion of the vacuum jacket surrounding the end of line I 4. A glass aeoaaeez tube .39 `.providedlwith` a neoprene .stopper 4011s.` clamped'to the Asteinof.. the pipettelso that the. stoppersealsthe bottom of thepipette.` .When
the desired `fractioniorfanypart thereof has been distillate are not required, a Mohr typecpipette which isheat sealed. `at it'slower end, may be 1arlinewlt.; il* Y.,
f. Water may rangedito collect. the condensate delivered through ture of lthe water, itlmayibe precooled, `orother e'oolingfflu-idsimay 4be employed and may be precooled if .desiredr` Air-isa suitable coolingmef dium ,for .usein :the` primaryfcondenser when fractionatingv liquidsJhaving boiling points in excess'ofthetemperature of the air employed. The air 'advantageously is supplied through` a control valve from a constant-pressure source, and it maybe preccoled,-if desired, depending on the condensation temperature of :the liquids lbeing` fractionated. VLWhen fractonating more. volatilev liquids,A other .eoolinguids precooled, if desired, may be :utilized in the primary condenser..` .l Measav urement of the quantity and speed of the cooling fluid passing through the primary condenser may be `indicated by the use of a standard flowmeter.
`In. thei Voperation 4:of the still illustrated,` `the charge measured volumetrcally or gravimetrical-` lypis placed in the `still pot I6, the pot isconnected to the1fractionating tube` I; current ,is
supplied to heater I8, and the boil-up rate isad-V justedl to` the desired value, e. g., about` ten drops` per Vminute run-back. While` thus adjusting the.
boil-.up ratefyby,varying` the heat input tothe pot, sufiicient air. or other suitable cooling fluidl is passed throughthe'jacket-of primarycondenser 2 to condense all theup-rising vapors,.coil 26 having been put into rotation upon evidence of boil.- ing` inthe pot. The true overhead vapor temperature, is indicated by` `thermocouple 5, this thermocouple being positioned at` the lowermostA endof thermowell 1, which end may be located.. e. -g.about 10 mm. above the top ofwrctating coil and about mm. below the bottom of the jacket` of the primary` condenser. After the desired boilupv rate has been established and the vapor temperature labove coil 26 has come to equilibrium, the rate of flow of cooling `medium through the jacket of condenser 2 is gradually reduced until therrriocouple` 6 indicates that vapor is passing through this condenser.l Sufllcient cooling uid passes through the jacket of cold finger condenser 3 toi condense all vapor passing the primary condenser. ABy further regulation of the flow of cooling fluid through the primary condenser, the desired overhead take-off rate may be established,'the indication of thermocouple B serving asa guide in effeetingthis regulation. The pot heat input is increased during the course of the fractionation to maintain the required quantity of boil-up. The current supplied to the heating element 33 of vacuum jacket 30 is controlled to maintain a minimumtemperature difference -between it and the vaportemperature. Fractions` orfcuts of fractions of the material being distilled maybe removed periodically by changing the colbe employedieffectively asthe coole. ingzlmedium in :fthe total` condenser,.when` frac-k.l tionating liquidsehaving boilingy points` infexcess; of the temperature of the: water: InfractiomT ating .lmoreivolatileafliquida e. guthose having.: boiling points flower 4than the .normal tempera-.-`
lection ltube .391 or other. receiver as r1 previously.: described, ...lim f., `The `.provision of the..primarycondenseri'in combination iwith the final cold' fingercondenser.` 'i
5 not only.;v enables .equilibrium condtionsto be :es-.r tablished within-the .columrivbefore take-off com. densationis started, but alsoA enables `jpredetere: mined and accuratecontrol ofthe take-off `irate.` In;` this manner any desired reflux ratio may. be
10 achieved. Also, use of the primary condenser. to` control `.the reflux ratiolprovides an .automatic indication of the end of the-fractionationycf. one. component,` since the, take-off irate willdecrease andthereiiux .ratio will increase at this end point? and i since the primary. condenser must. heat. up .u
to the vaporization temperatureot the'succeec'ling.`
ing an internal diameter of 2.75 mm. and `with.`
a rotating element of 2.7 mm. diameter, :and utilizing rotating` element speeds varying -from about 1860 R.` P..M. to about 2260 R. P. M., the. 30.` theoretical plate value` eiciencies were deter-i mined to range from about` 130 to about l00,with boil-up rates varying respectively from about 0.07' m1. per minuteto about'0.20 ml; per minute. Re-
sults obtained during routine fractionationsin D. columns of the present invention provided 'with fractionating tubesA having internal :diameters:V ranging from 2.801mm. up to 3.10 mmandwith rotating elements having a diameter of V2.7 mm., have shown no marked differences whencompared 40 with acolurnn provided with a-fractionating tube having an internal diameter of 2.75 mm.` and with a rotating element having a diameter of 2.7
An embodiment of the apparatusiofthe present invention may also'be `used in vacuum fractiona-` m tion'fif means areprovided `for the transmission. into the evacuated space ofthe mechanical power required `to rotate the 4helical coil.' lSuch means may be a conventional-packing, such as isidescribed in the aforementionedv Svensk KemfTids.A reference, ibutis preferably that described inthe i JohnJ. Piros application entitled"Non-Leaking Rotary Seal, Serial No. 80,795, led of evendate herewith and issued as Patent No. 2,560,660.- Figs. 2 and 3 of the drawings illustrate such an apwparatus.- i r w o In Figs. 2 and 3, the fractionating'column con` sists of a 10 mm. heavy-wall. Pyrex glass tube 4I having an internal diameter of 5.9-6t0l mln.i and having a length of about cm. `Above the tube oare two condensers, a primary or partial condenser 42 and a nal or total condenser 43. The partial condensers purpose is to provide the required reflux for column'operation by coni densing a part of theboil-up. By regulating the 5 rate of air passing through this condenser, using connections 4l and 45, the amount of vapors allowed to get past the partial condenser to the total condenser above it is controlled. 'Ihepartial condenser has an opening rthrough its rentire' length which allows a rotating tungsten shaft `4i to pass through itrand extend into therotatingv part of the rotary seal where it is held in placel by a small setscrew 41. The total condenser .isL a double helical coil through which the cooling medium. wateror air, passes, thecoolinglmedium .turned on when there is evidence of. boiling` in the pot. After the proper boil-up rate has been established and the vapor ,temperatureA `abovethe vpacking has-come to equilibrium, ,thearrate through the partial condenser is slowly )cutback until the desired overheadtake-.off rate isreached.
When tested, the vacuum still .describedsucf cessfully handled charges :off-5:40 ml.; operating l at pressures from 'atmospheric to ,less thanone fmm. of mercury absolute and at temperatures from room temperature to over 500 F. at the head. Using dibutyl phthalate the hold-up was found to be between 0.5-0.7 ml. at normal boilup rates and at one mm. of mercury absolute head pressure. The normal boil-up rate ranged from 40-120 ml. of liquid per hour, and for efiicient fractionation, the take-off rate was held below two ml. per hour. At total reflux and at 40 ml. of liquid per hour boil-up, the column tested at l55-6lltheoretical plates at atmospheric pressure,
and at one mm. of mercury absolute pressure with a 60 ml. of liquid per hour boil-up and take-off rate of 0.40 ml. per hour the column had an eniciency of about 20 theoretical plates. At a 40 ml. of liquid per hour boil-up rate of dibutyl phthalate at one mm. of mercury at the head, the pressure drop through the column was 1.5 mm. of mercury.
This application is a continuation-impart of our copending application entitled MicrostilL Serial No. 721,656, filed January ll, 1947.
We claim :V
1. A laboratory micro-still for the fractional distillation of small quantities of mixtures of liquids having diiferent boiling points, comprising a still pot, a fractionating tube connected thereto, a rotatable elongated helical wire coil l disposed within said tube and having transverse major and minor axes, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major axis being less than the diameter of said fractionating tube, a condenser associated with said tube disposed above said coil and a take-off line for removing condensed vapors.
2. A laboratory vacuum micro -still for the fractional distillation of small quantities of mixtures of liquids having different boiling points, comprising a still pot, a fractionating tube connected thereto, a rotatable elongated helical wire coil disposed within said tube and having transverse major and minor axes, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major major axis being less than the diameter of said fractionating tube, means including a seal for rotating said coil, a condenser associated with said tube disposed above said coil and a take-off line for removing condensed vapors.
3. A laboratory micro-still for the fractional distillation of small quantities of mixtures of liquids having different boiling points, comprising a still pot, a fractionating tube connected thereto, a rotatable elongated helical wire coil disposed within said tube and having transverse major and minor axes, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major axis being less than the diameter of said fractionating tube, band means mounted within said coil for the support thereof, a condenser associated with said tube diposed above said coil and ia fractiqiardi'stuiatipn of Smau quantities of mixv sion on the transversemajo l Y jjthe 'diameter Vof 4saidj 1fraction ting tubeigband 1 Ineens mounted-within saidcoi-lllfor thefsupport tures of liquids 'having different boiling points, comprising a still pot, a fraotQneting tube connected thereto, a `rotatableelong`ated helical wire coil disposed within said tube andhavingftransverse major and minor axes, its-dimensin on :the transverseA major axis greatly exceeding its dimension on the transverse `minor axis, its` dimen- Xie beirlslelssthan thereof, "means including a 'seal for rotatingisaid coil, a condenser associated with said tube disposed above said coil and a take-off line for removing condensed vapors.
5. A laboratory micro-still for the fractional distillation of small quantities of mixtures of liquids having different boiling points, comprising a still pot, a fractionating tube connected thereto, a rotatable elongated helical wire coil disposed within said tube and having transverse major and minor axes, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major axis being less than the diameter of said fractionating tube. band means mounted within said coil for the support thereof, a primary condenser associated with said tube disposed above said rotatable coil and arranged to return all vapor condensed thereby as reflux, a take-oil line, a total condenser disposed above said primary condenser and arranged to deliver all vapor condensed thereby to said takeoff line, and means for rotating said coil within said tube.
6. A laboratory micro-still as defined in claim 5, including an integral vacuum jacket substantially enclosing said fractionating tube, primary condenser, total condenser and take-off line, said jacket being silvered internally with the exception of that part thereof surrounding said takeoff line.
7. A laboratory micro-still as dened in claim 5, including an integral vacuum jacket substantially enclosing said fractionating tube, primary condenser, total condenser and take-01T line, and a thermowell entering said vacuum jacket near the top thereof and passing through said jacket and into the vapor zone at a point below the end of the primary condenser.
8. A laboratory micro-still for the fractional distillation of small quantities of mixtures of liquids having different boiling points, comprising a still pot, a fractionating tube connected thereto, a rotatable elongated helical wire coil disposed within said tube and having transverse major and minor axes, its dimension on the transverse major axis greatly exceeding its dimension on the transverse minor axis, its dimension on the transverse major axis being less than the diameter of said fractionating tube, band means mounted within said coil for the support thereof, a primary condenser associated with said tube disposed above said rotatable coil and arranged to return all vapor condensed thereby as reflux, a take-off line, a total condenser disposed 1 above said primary condenser and arranged to deliver all vapor condensed thereby to said takeoff line, and a rotatable shaft extending through an opening through the entire length of said primary condenser, said shaft being connected to said rotatable coil.
1 1 9. Aflaboratcry micro-still as denedin claim 8, in which said total condenser isformecl of two helical coils having atxheir-junction adripper.
YJOHN J. PIROS.
n l REFERENCESQITED .Q l iThepfcllwing*references are of recordiin .the
l liilefof this patent: 1
'Y UNTEDSIfATES PATENTS `'Number f 5 Name Date y 1,917,272 Podbehiak` Jnlyfll,v v1933 f- 2,400,021V Podbielnak .May '7, 1946 12,415,411
Bowman.. Feb. 11, 1947.15
12 .c OTHER- REFERENCES Y Svensk.' Kem. Tids., vol. 55 V`(19.476), pages: 145- V150 ;4 abstracted' Chemical Abstracts; v01. 40, co1- umn 5962.
Koch et a1.:` Die Chemische "Fabrik, vol. l14. (1941) pages 387-390. i
Bureau of Mines Technical Paper No. 600, pages