Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D1/00—Evaporating
  • B01D1/22—Evaporating by bringing a thin layer of the liquid into contact with a heated surface
  • B01D1/222—In rotating vessels; vessels with movable parts
  • B01D1/223—In rotating vessels; vessels with movable parts containing a rotor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B5/00—Other centrifuges
  • B04B5/02—Centrifuges consisting of a plurality of separate bowls rotating round an axis situated between the bowls
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04B—CENTRIFUGES
  • B04B5/00—Other centrifuges
  • B04B5/04—Radial chamber apparatus for separating predominantly liquid mixtures, e.g. butyrometers
  • B04B5/0407—Radial chamber apparatus for separating predominantly liquid mixtures, e.g. butyrometers for liquids contained in receptacles
  • B04B5/0414—Radial chamber apparatus for separating predominantly liquid mixtures, e.g. butyrometers for liquids contained in receptacles comprising test tubes
  • B04B5/0421—Radial chamber apparatus for separating predominantly liquid mixtures, e.g. butyrometers for liquids contained in receptacles comprising test tubes pivotably mounted

Definitions

• This invention concerns centrifugal evaporators.
• centrifugal evaporators compared with some other forms of evaporators such as rotary evaporators or vortex evaporators is that they evaporate liquids more slowly. This is in some measure due to the lack of agitation of the liquid in such machines.
• sample tubes are held in a block to which orbital motion is imparted, and thus also to the sample tubes, which causes the liquid in each of them to form a vortex in the tube, as illustrated.
• rotary and vortex evaporators Another advantage of rotary and vortex evaporators is that the liquid is continuously mixed so that the evaporating surface is continually refreshed, and compositional variations in the bulk of the evaporating liquid are avoided. This means that the bulk liquid has substantially the same composition as that in the surface and will be maintained at substantially the same temperature.
• rotary and vortex evaporators suffer from at least one disadvantage, when compared with centrifugal evaporators, namely that the evaporation pressure must be manually controlled, not only to allow evaporation to take place, but also to avoid boiling of the liquid which, in the absence of applied other forces, such as centrifugal force in the case of a centrifugal evaporator, would cause liquid to be ejected from the sample tube.
• the present invention seeks to provide an apparatus and method by which the liquid in a tube, well or other container undergoing centrifugal evaporation, is caused to be agitated in such a manner as to increase the surface area of contact between the liquid and its container and to provide continuous replacement of the evaporating liquid surface layer with liquid from regions below the surface layer, in order to achieve the advantages enjoyed by the other evaporation methods mentioned above (and in particular to realise faster evaporation rates) whilst at the same time retaining the advantage of spitting suppression by the application of a sufficient centrifugal force.
• the invention also seeks to provide for improved mixing in a sample liquid, in order to reduce local superheating in the bulk of the liquid below the surface layers and compositional variation of the bulk liquid, thereby reducing still further the tendency for liquid to be ejected, by spitting, from the tube.
• a centrifugal evaporator typically includes multiple sample tubes (which expression can mean other forms of sample holder such as vials or wells sunk into solid blocks) which are held in a holder and spun with the sample tube axes in a fixed relationship to the axis of rotation of the evaporator, either normal to the axis of rotation of a sample tube holding rotor (hereinafter referred to as the rotor axis) as illustrated in Figure 2a, or at a fixed angle not equal to 90° as shown in Figure 2b.
• sample tubes which expression can mean other forms of sample holder such as vials or wells sunk into solid blocks
• a method of performing centrifugal evaporation of a sample contained in a tube having walls and supported in a holder comprising the steps of mounting the holder on a rotor which is rotatable about a vertical axis within a vacuum chamber, rotating the rotor about its axis with the tube inclined relative thereto, and simultaneously causing the holder to perform a cyclic movement relative to the rotor, such that the tube moves from a first position with one wall nearest the rotor axis to a second position with the opposite wall nearest the rotor axis.
• a centrifugal evaporator comprising a holder supporting at least one sample tube and mounted on a rotor within a vacuum chamber; first drive means for rotating the rotor about its vertical axis; mounting means for movably mounting the holder so that the tube is inclined relative to the rotor axis; and second drive means for causing the holder to perform a cyclic movement about the mounting means; whereby the tube is caused to move from a first position in which one wall portion thereof is nearest to the rotor axis to a second position in which the opposite wall portion is nearest the rotor axis.
• the mounting means may comprise a plate secured to the rotor and an arm secured to the holder and connected to the plate by a pivot, enabling the holder to move from a first position in which the axis of the tube is at an acute angle to the rotor axis to a second position which the axis of the tube is at an obtuse angle to the rotor axis.
• the holder may be secured to a drive shaft rotatably mounted from the rotor, the second drive mean causing rotation of the drive shaft.
• the invention thus provides practical means for rotating such multiple sample tubes about their own separate axes, or subjecting them to oscillatory motion, in addition to subjecting them to rotation about the rotor axis for achieving the desired increased contact area with the sample tubes and mixing of the sample liquid.
• the angle at which the axis of each tube is held, relative to the rotor axis of rotation, is changed while they are rotating.
• the liquid will rapidly adjust its position relative to the tube, so that the liquid is again positioned as far away as possible from the rotor axis. This means that the liquid will move to a different position in the tube, thereby extracting heat from a different part of the tube, and the free surface will consist of different molecules. Some mixing of the liquid will also occur.
• the inclined tubes are also continuously rotated about another axis which intersects the rotor in a manner which generates a cone, the liquid in the tubes will be swept around the inside of the tubes to simulate a vortex.
• the axis of the cone will itself be rotated, which will cause the liquid in each tube to be agitated, to increase its free surface area and extract more heat from the walls of the tube, thereby considerably increasing the rate of evaporation.
• liquid samples 1 are held in tubes 6 in swings or buckets 2 that pivot about pins 3 in a rotating plate or rotor 4.
• the liquid in each tube will take up the position illustrated in Figure 4(a).
• the buckets When the plane of the rotating plate is suddenly displaced downwards vertically (ie in an axial direction) the buckets will adjust their rotational plane correspondingly to the position illustrated in (c), but not immediately because of their inertia. Thus they will momentarily assume position (b) before moving to position (c).
• the liquid in the sample tubes 6 will adjust more rapidly to the change and will temporarily move towards the lower wall of the tube as illustrated in position (b).
• the rotation plane is then rapidly displaced upwards back to its original position, causing the liquid in the tubes momentarily to assume position (e) before returning to position (f), which is the same as the original position (a).
• the sample rotation plane can be moved by a variety of means, including moving the entire apparatus, moving the drive shaft on which the rotor rotates, or moving the rotor relative to the drive shaft.
• the mechanisms described above achieve movement of the tube holder axes in one plane, which also contains the axis of rotation. If the tube axes are simultaneously moved in a plane that is normal to the axis of rotation the tube axes can in fact be made to move in a conical manner, as referred to above, and better results can be obtained.
• One method for achieving this movement is to hold the sample tube holder so that the tube axes are inclined at an angle of about 45° to the axis of rotation and rotate the holder about its own axis. This action will cause the tube in the centre of the holder to rotate about its own axis and the axes of the outer tubes will rotate in a manner which describes a cone: they will also be displaced from their original position.
• the angle at which the tubes are held can be varied from, for example, 35 to 55 degrees. Angles outside this range are also possible but require tubes to be less fully filled to avoid liquid spillage.
• Sample tubes 61 are held within a surrounding vacuum chamber 76 in one or more holders 62 attached to sample holder stiafts 63 which are held in a rotating gearbox 64 and which are each mounted in a bearing 65.
• the bearing contains a means (not illustrated) of locating the shaft 63 axially and a seal 66 to seal the inside of the gear box 64 from the space outside the gearbox.
• Each shaft 63 has a bevel gear 67 which is attached to the end inside the gearbox, and the gear 67 meshes with another bevel gear 69 which is attached to a spindle 70.
• the spindle passes down through the centre of a main drive shaft 71 through bearings (not shown) to a pulley 72, which is driven via a belt 85 and smaller pulley 86 by a motor 87.
• the drive shaft 71 is connected to the gearbox 64 by screws or other means (not shown), and is supported in a drive support 73 by means of upper and lower bearings 74a and 74b.
• a seal 75 above the upper bearing 74a seals the drive shaft 71 from the vacuum chamber 76, and a shoulder 77 below the lower bearing 74b and a circlip 78 above the bearing 74b axially locates the shaft 71.
• the drive support 73 is held in the chamber by means of screws 79, and an O-ring seal 80 seals the inside of the drive support from the vacuum chamber 76.
• the drive shaft 71 is attached to a pulley 81, which is driven via a belt 82 and a smaller pulley 83 by a motor 84.
• samples containing the non-volatile substance, and a volatile liquid in which it is dissolved or otherwise mixed are placed in the tubes 1 which are placed in holes in the holder 62 or, alternatively, the liquid sample is placed directly in holes in the holder 62.
• the whole gearbox assembly 64 is then made to rotate, by applying suitable power to the motor 84, at a speed which will provide enough centrifugal force to the samples to prevent sample loss from the tubes when the chamber 76 is evacuated. Power is also applied simultaneously to the motor 87, which will cause the samples to rotate about the axes of the sample holder shafts 63.
• the rotation of the gearbox will normally be at a speed which will apply 50 - 200g centrifugal force to the samples at say 200-750 rpm, depending on the size of the equipment.
• Rotation of the samples about the sample holder axis will normally be at a much lower rate say 25 to 150 rpm and controlled by setting the relative speeds of motors 84 and 87.
• the chamber is evacuated to a pressure that will cause evaporation of the sample liquid. It may also be necessary to apply heat by means that are well known in centrifugal evaporators.
• the invention has been described in relation to centrifugal rotation of the sample tube holders in combination with rotation or orbital motion of the individual holders, the invention is not limited to unidirectional rotation of the individual tubes, and advantageously, the tubes may instead be subjected to an oscillatory rotational motion, so that the tubes do not continue to rotate in one direction.
• the motor 87 may be a reciprocating drive. This simplifies the making of electrical connections to sensors in or on the tubes, and avoids the need for slip-ring connections, eg between the gearbox 64 and the tubes 61, since flexible electrical cables can accommodate the oscillatory motion.
• Slip-ring connections, or a radio link will in general be necessary to complete the signal path (and/or supply of power) to sensors (not shown) in or on the tubes, as between the shaft 71 and contacts on the stationary vacuum chamber 76 ( Figure 6), or to an external receiver which may be inside or outside the chamber 76.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)

Applications Claiming Priority (7)

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• 2000
  • 2000-01-21 EP EP00900739A patent/EP1069956A1/de not_active Withdrawn
  • 2000-01-21 WO PCT/GB2000/000172 patent/WO2000047327A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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