US3347754A

US3347754A - High vacuum distillation

Info

Publication number: US3347754A
Application number: US372170A
Authority: US
Inventors: Thomas William Llewelyn
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1963-06-21
Filing date: 1964-06-03
Publication date: 1967-10-17
Anticipated expiration: 1984-10-17
Also published as: BE649513A; DE1519557A1; FR1398381A; GB1062032A

Description

Get. 17, 967

W. L.. THOMAS HIGH VACUUM DISTILLATION Filed June 5, 1964 FIG.

7`0 vacuum pump 5 Sheets-Sheet l 2616: fric .4 @aa/5* @wif/MM ZAM INVENTOR w|| l |AM LLEWELYN THOMAS MORGAN, FINNEGAN, DURHAM a PINE ATTORNEYS @et 1'?, 1967 w'. L. THOMAS 3,347p754 HIGH VACUUM DISTILLATION Filed June s, '1964 .5 sheets-Sheet 2 MORGAN, FINNEGAN, DURHAM 81 PINE ATTORNEYS Filed June s, 196,4

(an, fda! bade/151k? W. L. THOMAS HIGHVACUUM DISTILLATION 3 Sheets-Sheet 3 MORGAN, FINNEGAN, DURHAM 8P|NE ATTORNEYS United States Patent 3,347,754 HIGH VACUUM DISTILLATION William Llewelyn Thomas, Sunbury-on-Thames, Middlesex, England, assigner to British Petroleum Company Limited, London, England, a corporation of England Filed `lune 3, 1964, Ser. No. 372,170` Claims priority, application Great Britain, June 21, 1963, 24,778/63 6 Claims. (Cl. 202-186) ABSTRACT OF THE DISCLOSURE A multi-stage centrifugal still having a series of concentric vaporisation zones and which has the special feature that liquid phase material (input material in the case of the rst zone, otherwise condensate) is added to each zone at the upstream periphery and removed at the downstream periphery.

The invention provides a simple and convenient construction in which a rotary vaporiser is divided into a series of concentric vaporisation zones each having a drainage tube at its outer periphery. Above each zone there is situated a condenser tray which slopes downwards towards the next vaporisation zone and which terminates in an edge for dripping condensate into the upstream periphery of that zone.

This invention relates to high vacuum distillation apparatus of the type in which a vaporiser having a vaporising surface and a condenser are provided and separated Aby substantially unobstructed space, distilland being spread over the vaporising surface in the form of a thin lm. In particular this invention relates to centrifugal stills of the above type, i.e. stills in which the vaporising surface is in the form of a rotatable disc so that distilland introduced onto the surface is dispersed in lm form over the surface by centrifugal action.

Distillation apparatus of the above type is well known and is particularly suitable for distilling, under a high vacuum of the order of 1 micron Hg, thermally unstable materials. In apparatus of this type the distilland is heated for a short time only. Distillate is condensed on the condensing surface and removed from the system; undistilled residue is also cooled and removed.

According to the present invention, in a high vacuum centrifugal distillation apparatus of the above type, the vaporising surface of the vaporiser is divided into a series of concentric vaporisation zones each zone being provided with a drainage conduit situated near its outer periphery land adapted to remove surplus liquid from the zone, the inlet conduit is positioned so as to introduce distilland near the inner boundary of the inner zone and the condenser comprises a series of condensing trays, one for each vaporising zone, the trays sloping downward towards the outer circumference of the vaporiser and having an outer edge positioned, in the case of all trays except the last, over the next succeeding vaporisation zone near its inner `boundary and, in the -case of the last tray, over a collecting zone, each tray being adapted, in the use of the apparatus, to condense vapour from its associated vaporising zone and to deposit said condensate from its outer edge.

The distance between the vaporising and condensing surface preferably approaches the molecular mean free path of the vapour molecules at the operating pressure. Desirably this distance is less than the molecular mean free path.

The vaporisation zones may be defined by rings or corrugations formed on the vaporising surface.

The condensing trays mounted on the condensing surface are preferably inclined as steeply as possible consistent with the mechanical limitations imposed by the distance between the vaporising and condensing surfaces, by the height of the rings defining the distillation zones and by the angles of inclination of the vaporising and condensing surfaces themselves. The greater the inclination of the condenser trays the less is the tendency for condensed distillate to drop back into the zone from which it has just been distilled.

The vaporising surface may be horizontal although preferably this surface is inclined upwardly from the centre, the angle of inclination to the horizontal increasing with the diameter of the vaporising surface. The maximum practical diameter for horizontal vaporisers is of the order of one foot. At greater diameters the centrifugal force tends to pull the distilland into a series of radial streaks so that the total area of the rotary vaporisng surface is not utilised ediciently. Reducing the speed of rotation of the vaporiser or increasing the flow of distillant, although ensuring a continuous film at the periphery of the vaporiser, gives rise to poor conditions in the central area where the distilland forms thick layers. These ditliculties may be overcome by inclining the vaporising surface upwardly from the centre, centrifugal force at the periphery being smaller for a given surface area and speed of rotation in the case of an inclined plate than for a horizontal plate. Even in apparatus where the vapo rising surface is less than one foot in diameter the plates may advantageously be inclined. Thus a small laboratory apparatus having a 5 inch diameter vaporiser may suitably be inclined at an angle of the order of 15 to the horizontal. Large apparatus, for example having a vaporiser with diameter of the order of 5 feet may be inclined at an angle of -85 to the horizontal, intermediate sizes being inclined at intermediate angles. By inclining the vaporising surface in this manner a thin film of distilland can be maintained on the entire vaporising surface.

The vaporiser preferably takes the form of a circular disc and any convenient means of heating the vaporser may be employed. For example, a hot medium such as oil may be circulated through the disc. Preferably, however, an electrical heating element is incorporated in the disc.

Preferably the area of each vaporisation zone is equal to or greater than that of the next succeeding vaporisation zone. The factor determining the optimum areas in each Case is the liquid loading in each zone. It is desirable that the evaporating area of a zone should be directly proportioned to the liquid loading in that zone so as to maintain the film thickness and residence time constant over the entire vaporising surface.

The condenser may be cooled by any convenient means. Preferably, however, means are provided to allow for the circulation of a coolant medium such as air or particularly water through the condenser.

In stills according to the introduced to the centre of `from the vaporiser. This procedure is repeated from zone to zone until the last zone. From here, the distillate is product, the residue being removed :as before. The collected residues from each zone may be recycled or not depending upon whether it is required to fractionate completely a batch of feedstock or whether continuous separation of a distillate and residue is required.

Temperatures may be measured in such parts of the apparatus as may be required by any suitable means, for example by means of thermocouples.

One embodiment of the present invention is illustrated with reference to the accompanying FIGS. 1 and 2.

FIG. 1 is a front view, partially in section, of a distillation apparatus according to the present invention having a horizontal vaporiser.

FIG. 2 is a side view of the apparatus of FIG. 1.

FIG. 3 is a front view of a vaporiser and condenser which are inclined as hereinbefore described.

In FIGS. 1 and 2, the apparatus comprises a glass vessel 1 having formed in it a gutter 2 which has a slight downwards inclination towards a tap 3. Tap 3 is of a two-way type which permits passage of liquid entering from upper limb 4 either back to the vessel via lower lim'b 5 or to a receiver (not shown) via limb (a. At the base of the vessel, tube 7 is provided for charging feedstock to the apparatus and for draining the apparatus when required. The vessel is provided with a top plate 9 and is sealed against this by a rubber gasket 10. Pipe 8 passes through the top plate 9 and is connected in the normal manner to a diliusion pump backed by a rotary vacuum pump (not shown). The vessel contains a circular, rotary, castaluminium vaporiser 11 incorporating an electrical resistance heating element 12. The vaporiser 11 is connected by shaft 14 to a motor (not shown). Leads 13 connect heating element 12 through the shaft 14 to slip rings (not shown) outside the vessel. Shaft 14 is sealed from top plate 9 by vacuum seal 15. Concentric rings 16a, b, c are formed on the upper surface of the vaporiser 11 dividing the vaporiser into annular zones. Duets 17a, b, c pass through the vaporiser at a number of points around the outer periphery of each annular zone. Circular condenser 1S is located above and parallel to the vaporiser land is provided with a central hole 18 through which shaft 14 passes. Inlet and outlet tubes 19 and 2t) respectively are provided to permit circulation of coolant water through the condenser 18. Concertric trays 21a, b, c are formed on the underside of condenser 18 to form condensing zones corresponding with the distillation zones of the vaporiser. The outer edges of the trays 21 project slightly over the tops of the corresponding rings 16, the end of the linal tray projecting over gutter 2. Feed pump 22 is located in the base of the vessel 1 and is driven by shaft 23 which is itself enclosed in tube 24 and passes through top plate 9 via vacuum seal 25. Tube 24 serves to conduct liquid from the pressure outlet side of pump 22 up the annulus between the drive shaft 23 yand the tube 24 and has an inlet conduit 26 which extends to a point near the centre of vaporiser 11 at 27. Residue receiver 28 is supported by tube 24 and has 'ball valve 29 at its base. Ball valve 29 is operated by plunger 30 which passes through a vacuum seal in top plate 9 and is connected to the ball valve 29 by lever arm 31. Ball valve 29 normally closes the upper end of receiver drain pipe 29'. Funnel 32 is `placed under vaporiser 11 and is supported by residue receiver 28.

Vessel 1 is evacuated to l0 microns Hg or less via pipe 8 and feedstock is introduced slowly via tube 7, degassing of feedstock taking place at this time. Feed pump 22 and vaporiser 11 are set in motion and feedstock is circulated over the vaporiser. Application of heat to the vaporiser at this stage assists degassing.

Initially the temperature of the vaporiser is so low that no vaporisation occurs and the entire distilland passes over the inner zone of the vaporising surface of the vaporiser in a thin film to the inner ring or corrugation 16e then falls under gravity through the ducts 17e around the outer periphery of the inner distillation zone iir-stly into the funnel 32, then into the residue receiver 28 and thence through receiver drain pipe 29 into the base of the vessel 1. As the vaporiser temperature increases, some distillation, particularly of the more volatile components of the feedstock, occurs and the vapours formed con dense on the inner tray 21C. The condensate runs down the surface of the tray and drops on to the middle distillation zone near its inner periphery. This liquid passes in a thin lilm covering the middle distillation zone, to the middle ring 16b and is heated in the process. Some vaporisation, particularly of the more volatile components of the feed, occurs and these vapours condense on the middle tray 2lb. The unvaporised liquid from the middle distillation zone passes through the ducts 17b around the outer periphery of this zone, irstly into the funnel 32, then into the residue receiver 28, and finally into the base of the vessel 1. The condensed vapours from the middle tray run down the surface of this tray and drop on to the outer distillation zone near its inner periphery. This liquid pas-ses in a thin film covering the outer distillation zone, to the outer ring 16a and is heated in the process, Some vaporisation, particularly of the more volatile components of the liquid, again occurs and these vapours condense on the outer tray 21a. The unvaporised liquid from the outer distillation zone passes through the ducts 17a around the outer periphery of this zone, firstly into the funnel 32 then into the residue receiver 28, and thence into the base of the vessel 1. The condensed vapours from the outer tray run down the surface of this tray and drop into the gutter 2. The distillate that collects in the gutter runs down by gravity to the upper limb 4 which leads to the tap 3. At the `beginning of a run the tap is adjusted so that the distillate passes back to the vessel 1 through the lower limb S. Gradually the temperatures rise, and when they have reached their desired values the tap 3 is turned so that distillate runs through tube 6 into an external distillate receiver (not shown). In the preferred method of operation the ball valve 29 is now shut so as to collect the residue from vaporiser 11 in the receiver 28. Distillation is continued until all the feedstock has been pumped from the lower part of the vessel 1. The distillation may be terminated at this stage, if desired. If required, however, a series of distillate fractions may be prepared by repeated distillation, at successively higher temperatures, of the residue remaining in the still after the iirst distillation. The procedure then is to replace the lirst distillate receiver with another after all the feedstock has been pumped from the vessel 1. The ball valve 29 is opened, allowing residue to pass to the base of the vessel. This residue now forms the distilland for the next stage of the distillation which is carried out at a somewhat higher temperature than before. When temperature conditions have become steady, the second distillate is collected in the distillate receiver and the second residue is collected in the residue receiver 28. This procedure is repeated as many times as necessary. Eventually the distillation is terminated, the power is switched off, the still is allowed to cool, the vacuum is released, and the final residue is run olf from the residue receiver 2S into a sample container. The still may then be cleaned out with a suitable solvent.

In the embodiment of the invention illustrated in FIG. 3, the vaporiser 11 is inclined upwardly from the center, the condenser 18 being correspondingly inclined upwardly. By thus inclining the vaporiser, its upper or vaporising surface is correspondingly inclined and a thin tilm of distilland can be maintained on the entire vaporising surface without the distilland film being pulled into a series of radial streaks and Without the distilland being formed into thick layers in the central area.

I claim:

1. A high vacuum centrifugal distillation apparatus comprising a rotatable vaporiser having a vaporising surface, a condenser and an inlet conduit for introducing distilland to said vaporising surface, said vaporiser and condenser being separated by substantially unobstructed space, and wherein said vaporising surface is divided into a series of concentric vaporisation zones, each zone being provided with a drainage conduit situated near its outer periphery and adapted to remove surplus liquid from the zone, and wherein said inlet conduit is positioned so as to introduce distillaud near the inner boundary of the inner zone and the condenser comprises a series of condensing trays, one for each vaporising zone, the trays sloping downwardly towards the outer circumference of the vaporiser and having an outer edge positioned, in the case of all trays except the last, over the next succeeding vaporisation zone near its inner boundary and, in the case `of the last tray over a collecting zone, each tray being adapted, in the use of the apparatus, to condense vapor from its associated vaporising zone and to deposit the condensed vapor from its outer edge.

2. An apparatus as claimed in claim 1 wherein the vaporisation zones are in part defined by rings formed on the vaporising surface.

3. An apparatus as claimed vaporising surface is inclined upwardly from the centre -at an angle of between 15 and 85 to the horizontal.

4. An apparatus as claimed in claim 1 wherein an electrical heating element is incorporated in the vaporiser.

in claim 1 wherein the 5. An apparatus as claimed in lclaim 1 wherein the area of each vaporisation zone is at least equal to the area of the next succeeding vaporisation zone with respect to distilland flow.

6. An apparatus as claimed in claim 1 wherein the condenser incorporates means to allow for the circulation of `a uid coolant medium therethrough.

References Cited NORMAN YUDKOFF, Prmury Examiner. I. SOFER, Assistant Examiner.

Claims

1. A HIGH VACUUM CENTRIFUGAL DISTILLATION APPARATUS COMPRISING A ROTATABLE VAPORISER HAVING A VAPORISING SURFACE, A CONDENSER AND AN INLET CONDUIT FOR INTRODUCING DISTILLAND TO SAID VAPORISING SURFACE, SAID VAPORISER AND CONDENSER BEING SEPARATED BY SUBSTANTIALLY UNOBSTRUCTED SPACE, AND WHEREIN SAID VAPORISING SURFACE IS DIVIDED INTO A SERIES OF CONCENTRIC VAPORISATION ZONES, EACH ZONE BEING PROVIDED WITH A DRAINAGE CONDUIT SITUATED NEAR ITS OUTER PERIPHERY AND ADAPTED TO REMOVE SURPLUS LIQUID FROM THE ZONE, AND WHEREIN SAID INLET CONDUIT IS POSITIONED SO AS TO INTRODUCE DISTILLAND NEAR THE INNER BOUNDARY OF THE INNER ZONE AND THE CONDENSER COMPRISES A SERIES OF CONDENSING TRAYS, ONE FOR EACH VAPORISING ZONE, THE TRAYS SLOPING DOWNWARDLY TOWARDS THE OUTER CIRCUMFERENCE OF THE VAPORISER AND HAVING AN OUTER EDGE POSITIONED, IN THE CASE OF ALL TRAYS EXPECT THE LAST, OVER THE NEXT SUCCEEDING VAPORISATION ZONE NEAR ITS INNER BOUNDARY AND, IN THE CASE OF THE LAST TRAY OVER A COLLECTING ZONE, EACH TRAY BEING ADAPTED, IN THE USE OF THE APPARATUS, TO CONDENSE VAPOR FROM ITS ASSOCIATED VAPORISING ZONE AND TO DEPOSIT THE CONDENSED VAPOR FROM ITS OUTER EDGE.