New large-scale laboratory sublimer

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  • New largescale laboratory sublimerGilbert J. Sloan Citation: Review of Scientific Instruments 55, 1700 (1984); doi: 10.1063/1.1137605 View online: http://dx.doi.org/10.1063/1.1137605 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/55/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in New applications and control strategies for large-scale CPV plants AIP Conf. Proc. 1556, 266 (2013); 10.1063/1.4822246 Cyclone-anticyclone asymmetry of large-scale wakes in the laboratory Phys. Fluids 18, 036603 (2006); 10.1063/1.2179387 The new discussion of a neutrino mass and issues in the formation of largescale structure AIP Conf. Proc. 222, 521 (1991); 10.1063/1.40423 A largescale electroscope Phys. Teach. 19, 481 (1981); 10.1119/1.2340859 Large-Scale Electrical Demonstration Am. J. Phys. 32, 967 (1964); 10.1119/1.1970047

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  • New large-scale laboratory sublimer Gilbert J. Sloan

    Central Research & Development Department, E. l. du Pont de Nemours & Company, Experimental Station, Wilmington, Delaware 19898

    (Received 8 March 1984; accepted for publication 11 June 1984)

    A new sublimer is described, in which a glass condenser is surrounded by a close-fitting, rotating helical scraper of stainless steel. Sublimation takes place from an annular chamber below the condenser; sublimate is scraped from the condenser and falls through a central standpipe into a collection flask. The new device makes it easy to collect several fractions, of decreasing volatility, while maintaining condenser efficiency by avoiding accumulation of a thick layer of sublimate. Batches as large as 1 kg can be sublimed conveniently, at rates above 0.05 kg h -I.

    INTRODUCTION

    Sublimation is an old and widely used technique for purifica-tion of solids. Of the few works published recently on this subject, most deal with improved fractionation of small amounts of material (milligrams to grams).1 We describe here a device that allows rapid sublimation oflarger quanti-ties, and offers several other advantages.

    Conventional sublimers used by organic chemists are usually of glass, with a single condensing surface cooled in-ternally by a circulating fluid. 2 As sublimation proceeds, the effectiveness of the condenser diminishes because most or-ganic compounds have very low thermal conductivities. Moreover, the condensed solid is often hard and adherent to the condenser; these properties make it difficult to remove the sublimate and discourage the collection of multiple crops of sublimate, of decreasing volatility.

    The device described here uses a scraper to clear the surface of the condenser continuously and to deposit the sub-limate in a separate receiver in finely divided form. It is easy to change receivers to collect the sublimate fractionally.

    I. DESCRIPTION OF THE APPARATUS

    The central portion of the sublimer consists of a Pyrex body, 14-cm outer diameter and about 35 cm tall, with 0-ring flanges A and B at top and bottom, respectively (Fig. 1). The body may be fabricated from a commercially available resin kettle (Lab Glass, Inc., Vineland, NJ, No. LG-8075). The inner standpipe C is 4.1-cm outer diameter and about 15 cm tall; it is surmounted by a removable funnel D. Figure 2 shows the condenser assembly and the adapter which cou-ples it to the body shown in Fig. 1. The Pyrex condenser A (Fig. 2) is 4.5-cm outer diameter and about 20 cm long, below joint B (i'55/50, inner). The inner tube of the condenser is I cm in inner diameter and is terminated with joint C (i'24/ 25). Coolant enters the condenser through tubulation D and exits through E. The helical scraper is made of two stainless-steel bands F, 0.95 cm wide, welded to a hub at the bottom and to a ring G at the top; the inner diameter and outer diameter of the ring are 4.95 and 6.35 cm, respectively. A stainless-steel driveshaft H, 0.64 cm diameter, is attached to the hub ofthe helix by a setscrew. The scraper is centered at

    the bottom by a sleeve I of Teflon fluorocarbon resin, which makes a snug fit in the inner tube of the Pyrex contain-er; it is centered at its top by ring J, ofTeflon , which makes a snug fit on the outside of condenser A. Ring J is attached to stainless-steel ring G by three screws. Shaft H is sealed by an o ring in the two-piece adapter K, likewise of Teflon , which is sealed in joint C by two O-rings. The inner diameter of the helical scraper is about 4.7 cm. The condenser is mated with the joint of adapter L, which has a side port for evacua-tion, and the scraper is then mounted. Sublimand is charged into the annular chamber of the Pyrex body (Fig. I), funnel D is inserted, and the condenser/adapter assembly is then mounted on the Pyrex body; a receiver flask is attached to the lower flange of the body.

    A variable-speed motor is coupled to shaft H through a torque-limiting device. The latter is desirable to prevent damage to the glassware in case a rapid buildup of sublimate increases the torque required for its removal.

    ~-------4------~~~A

    D

    c

    B

    FIG. 1. Body of the scraped sub-limer: (A) and (B) O-ring flanges; (C) central standpipe for product collection; (D) funnel for product collection.

    1700 Rev. Scl.lnstrum. 55 (10), October 1984 0034-6748/84/101700-02$01.30 @ 1984 American Institute of Physics 1700

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  • H

    D

    J

    L

    E

    A

    G

    F

    I

    FIG. 2. Condenser and scraper assem-bly: (A) Pyrex Condenser; (B) and (C) 11' joints; (D) and (E) eollant inlet and out-let; (F) stainless-steel scraper bands; (G) stainless-steel ring; (H) driveshaft; (I) and (J) centeripg sleeves ofTeBon ; (K) sealing adapter for driveshaft, of TeBon ;(L) Pyrex adapter, to mate with lI'joint A (Fig. I). (Note: the lower Bange of the adapter is not shown in Correct size here; it must mate with Bange A of Fig. J.)

    1701 Rev. ScI.lnatrulIl., Vol. 55, No. 10, October 1984

    In use, an external heater tape provides the heat of sub-limation, and the scraper is rotated fast enough to assure that the condenser surface is cleared completely. Speeds of 1-25 rpm are commonly adequate.

    Several design variations are possible. Heat may be pro-vided by a permanent oil-filled jacket containing an internal resistance heater. The helical scraper may be replaced by a single ring, driven linearly over the condenser surface. In fact, this approach was tried before the helical scraper, but while workable, the ring tended to "stick" and move errati-cally.

    In use, sublimation starts at the outer wall, and heat transfer to the remaining sublimand through the internal vacuum becomes slower. This problem may be overcome by admitting a relatively conductive gas (helium) at modest pressure (one to a few Torr). The conductivity problem may also be overcome by mixing the sublimand with finely divid-ed, conductive material, such as metal beads or granules. Naturally, the chemical compatibility of the sublimand and the metal must be considered.

    II. APPLICATION

    Commercial 1, 6-hexanediamine (500 g, pale yellow) was charged into the annular sample chamber of the sub-limer. The apparatus was evacuated to 0.02 Torr, and gly-col-water coolant at -25 C was circulated through the con-denser. The scraper was rotated at 5 rpm, and the sublimand was heated at about 40 C. Colorless product was collected in the receiver. Sublimation was complete in 8 h, and a small amount of yellow-orange residue was left in the sample chamber.

    ACKNOWLEDGMENT

    I wish to thank the late R. J. McCarter for valuable suggestions and for skillful fabrication of the device de-scribed here.

    'K. Gosling and R. E. Bowen, Anal. Chern. 45,1574 (1974). 2R. J. McCarter, Rev. Sci. Instrum. 33, 388 (1962).

    Sublimer 1701

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