WO2011095756A1

WO2011095756A1 - Improvements relating to drying apparatus.

Info

Publication number: WO2011095756A1
Application number: PCT/GB2010/050900
Authority: WO
Inventors: Maurice Pitcher
Original assignee: Powder Systems Limited
Priority date: 2010-02-05
Filing date: 2010-05-28
Publication date: 2011-08-11
Also published as: GB201001895D0

Abstract

A vacuum drying apparatus (10) in accordance has a chamber defined by a chamber wall (12) which is disposed in housing (14).. Mounted to a wall of the chamber (12) are shelf supports (16) upon which shelves (18) are mounted. The shelf supports are mounted to chamber (12) by means of fixing means (20) hereto bolts (22) and (24). Surrounding securing bolts (22) and (24) is a shroud (26) integrally formed with the shelf support (16) the shroud (26) ensures that there are no exposed bolts and ensures that there is a seal between the interior of the chamber and the external environment. The chamber wall defines an open box having a roof, two side walls, a base and a rear wall.

Description

IMPROVEMENTS RELATING TO DRYING APPARATUS

The present invention relates to drying apparatus and methods of drying, more particularly, to drying apparatus and methods which are capable of drying chemical reaction products held in vessels.

Vacuum tray dryers are commonly used in the pharmaceutical processing of API (active pharmaceutical ingredient). Tray dryers are very commonly used in laboratory processes where small quantities of product are handled. To simplify scaling up to production processes where larger quantities are handled, tray dryers are also commonly used in production processes.

The process of vacuum tray drying involves the non agitated drying of a wet product cake where one or more solvents are removed from a compound under a partial vacuum. Application of vacuum reduces the solvent boiling point. Heating is then applied to provide sufficient latent heat of vaporization to convert the solvent from a liquid to gaseous state.

Drying pharmaceutical products at low temperatures is preferable because the compounds are typically temperature sensitive. Non agitated drying is often preferred because there is minimal alteration to the crystal morphology of the pharmaceutical compound. Crystal morphology greatly impacts the pharmacological effect of a compound. Unintended changes to morphology are not desirable.

It is an object of the present invention to overcome or alleviate one or more of the problems associated with the prior art.

In accordance with a first aspect of the present invention, there is provided a vacuum drying apparatus comprising a chamber sealable by a door, at least one shelf mounted within the chamber via a shelf support said shelf support and/or shelf having heating means disposed therein, and means for generating a vacuum.

The present invention is directed to relatively inexpensive drying systems which may be suitably employed, for example, to dry the reaction products of chemical synthesis.

The apparatus in accordance with the present invention will preferably provide a combination of moderate heat and reduced pressure to substantially accelerate the evaporation of liquids, typically solvents, from the trays which also contain a chemical compound of interest that is to be preserved.

The present invention provides a chamber within which the temperature and pressure maybe precisely controlled to facilitate drying of samples placed within the chamber. The present mvention involves an enhancement in the design of a pharmaceutical vacuum tray dryer and overcomes some shortcomings of the prior art.

Owing to the risk of cross contamination of different products, pharmaceutical processing equipment preferably must be readily cleanable. One preferred embodiment of the present invention has no exposed bolts, ledges, crevices. All of the surface of this embodiment are self draining and reachable for cleaning by an operator.

To protect operators from directly handling hazardous materials, process equipment like tray dryers are preferably suitable for access via barrier isolation devices like gloveboxes. Ergonornic concerns are critical for ease of operation of process equipment via gloveboxes. One embodiment of the present invention comprises shallow tray depths which ensure that all areas of the dryer are reachable to the operator. The apparatus may comprise a plurality of shelves.

The apparatus may comprise two or more shelf supports. Preferably the apparatus comprises two shelf supports. More preferably, each shelf has two supports and form a stack. The apparatus may comprise more than one stack of shelves.

Preferably, at least one shelf is mounted within the chamber by two shelf supports. Preferably, the shelf support comprises an elongate hollow member. More preferably, each shelf is integrally formed with the shelf support having a continuous cavity disposed therein such that heating means can be accommodated therein.

The cavity of the shelf support and/or shelf can be in fluid connection with one another such that a fluid and/or gas can flow there between.

The heating means preferably comprises the use of circulating fluid (eg water, ethylene glycol, synthetic thermal oils) and/or electric heating elements within the shelves. This provides direct tray heating whereby the heated shelves are in direct contact with the trays.

Preferably, the heating means comprises a conduit for circulating heat throughout the chamber and which is housed within the shelves and supports. Preferably the conduit comprises a pipe through which heating medium can flow.

The thermal fluid supply/return pipes may be directly welded to the shelves. The thermal fluid supply/return pipes may terminate in flanges which are bolted in place to the roof of the tray dryer chamber. The shelving stacks reside in a common tray dryer chamber. A front door maybe closable to create a sealed drying chamber. The chamber wall may have a cavity which can be insulated or heated. Product to be dried can be placed within trays which are then located on the shelves. An open design whereby all the trays reside in the same common chamber ensures uniform homogeneity of heating. The chamber walls may also be heated to provide indirect tray heating and prevent condensation forming on the chamber walls. In such an embodiment, the chamber is surrounded by a housing forming a cavity there between. This cavity may comprise heating means so as to reduce the risk of condensation and improve drying.

The present invention allows for aseptic and non aseptic processing. Sterilization can be conducted by dry heat sterilization and/or steam in place sterilization

The chamber preferably has a fluid and/or gas inlet and outlet to which the shelf support is mounted in fluid connection thereto. This enables fluid and/or gas to flow into the cavity shelf support and/or shelf itself and out of the cavity. This enables the shelves and chamber to be evenly heated to improve drying. In a preferred embodiment, the heating means comprises a heating medium conduit and this is in fluid connection with the inlet and outlet to enable heating medium to circulate therein.

Preferably the door, when closed creates a substantially hermetical seal.

In one embodiment, each shelf would typically support a single tray with front door access. Alternately, in another embodiment, each shelf would support 2 trays, a rear tray placed behind the front tray. A second, rear door would also be provided to allow access to the rear tray. Containment could be provided by front and rear gloveboxes In one embodiment, when heating with a circulating thermal fluid, the supply and return pipes, connected to the inlet and outlet respectively, can be an integral part of the shelves, welded in place to each shelf. The supply and return mounting flanges can both be located at the top of the shelving arrangement. The whole shelving assembly can be removed in one piece by unbolting the thermal fluid supply and return flanges. This overcomes some of the shortcomings of the prior art where heated trays are individually bolted to a supply and return pipe. Such prior art is a less cleanable design also requiring significantly more operator intervention to remove the trays for out of place cleaning and maintenance.

When heating via a circulating thermal fluid, the shelves may be internally baffled to distribute the flow of the thermal fluid and enhance the heat transfer performance. In another embodiment, the present invention can also be utilized for freeze drying. During freeze drying a deep vacuum is created to freeze the solvent. Heating is then applied to provide sufficient heat of sublimation to convert the solvent directly from a solid to gaseous state.

In one embodiment, a substantially laminar flow of dry inert gas is forced across the top of sample trays or plates placed within the chamber. The inert gas flow above the plates disrupts the accumulated vapor which can form above the chemical compounds and carries away the vapor, thus accelerating the drying process.

In one embodiment, the invention may suitably comprise a vacuum chamber with a temperature controlled heat source. Shelves within the chamber provide support for the sample trays containing the chemical compounds. The shelves are preferably located on shelf supports within the chamber.

Additionally, in a preferred embodiment, the shelves conduct heat to the trays of compounds which they support.

In accordance with a further aspect of the present invention, there is provided a method for drying a wet product cake by evaporating a solvent, comprising the steps of: a) placing said wet product cake within a vessel and placing said vessel upon a support within a vacuum chamber;

b) evacuating said chamber to reduce the pressure within the interior of said chamber to a desired value which accelerates evaporation, but which does not initiate boiling of the solvent;

c) supplying heat to said wet product cake without degrading said chemicals at said desired pressure; and

d) supplying a substantial flow of inert gas across the top of said plate.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which :

Fig. 1 shows a vacuum drying apparatus in accordance with the present invention. Fig. 2 is a cross-sectional view of the vacuum drying apparatus of Fig. 1.

Fig. 1 shows a vacuum drying apparatus 10 in accordance with the present invention and consists of a chamber defined by a chamber wall 12 which is disposed in housing 14. Mounted to a wall of the chamber 12 are shelf supports 16 upon which shelves 18 are mounted. The shelf supports are mounted to chamber 12 by means of fixing means 20 hereto bolts 22 and 24. Surrounding securing bolts 22 and 24 is a shroud 26 integrally formed with the shelf support 16 the shroud 26 ensures that there are no exposed bolts and ensures that there is a seal between the interior of the chamber and the external environment. The chamber wall defines an open box having a roof, two side walls, a base and a rear wall. The chamber can be sealed from the external environment by means of a door 38 (Fig. 2). Disposed on two of the shelves 18 are trays 36.

Disposed within the shelf support 16 is a cavity 28 which is in fluid commumcation with cavity 30 disposed within the integrally formed shelves 18. The points at which the shelf supports are mounted to the cavity wall also defines an inlet 32 and outlet 34. Inlet 32 and outlet 34 are in fluid communication with one another via the shelf support and the shelves cavities. Heating medium such as fluid and/or gas can enter the cavity via inlet 32 and circulate throughout the system exiting the cavity the via outlet 34. In a preferred embodiment, the cavity houses a pipe through which heating medium may pass and it is the pipe that is connected to the inlet and outlet.

The apparatus also comprises a pump for circulating the heating medium, means for heating the heating medium and a vacuum pump for creating a vacuum within the chamber (all of which are not illustrated).

Fig. 2 is a cross sectional view of the apparatus shown in Fig. 1 and shows the closable door 38 which selectively seals the cavity defined by cavity wall 12. As shown in Fig. 2 the shelves are supported by the shelf supports at an angle to the horizontal to facilitate draining when the apparatus is being cleaned.

The forgoing description of specific embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention. It is intended that the scope of the invention be limited only by the claims appended hereto.

Claims

1. A vacuum drying apparatus comprising a chamber sealable by a door, at least one shelf mounted within the chamber via a shelf support said shelf support and/or shelf having heating means disposed therein, and means for generating a vacuum.

2. An apparatus as claimed in claim 1 wherein the shelf and shelf support are integrally formed and define a cavity there between.

3. An apparatus as claimed in one or two wherein the chamber is surrounded by a housing forming a cavity there between.

4. An apparatus as claimed in claim 3 wherein the cavity comprises means for heating the wall of the chamber.

5. An apparatus as claimed in any one the preceding claims wherein the cavity between the shelf and the shelf support is in fluid connection with one another such that heating medium can flow there between.

6. Apparatus as claimed in claim 5 wherein the heating medium is a fluid and/or gas.

7. An apparatus as claimed in claim 6 wherein the heating medium is a fluid.

8. An apparatus as claimed in any one of the preceding claims having means for heating the chamber.

9. An apparatus as claimed in any one of the preceding claims having a vacuum pump for creating a vacuum within a chamber.

10. An apparatus as claimed in any one of the preceding claims wherein the shelf support comprises a means for mounting the support to the chamber wall.

11. An apparatus as claimed in claim 10 wherein the means for mounting the shelf support comprises a shroud which extends over the said means.

12. An apparatus as claimed in any of the preceding claims comprising two shelving supports each of which is mounted to a wall of the chamber and defines a cavity therein having an inlet and an outlet such that fluid can flow into one shelf support and out of the other.

13. An apparatus as claimed in any one of the preceding claims wherein the shelf is mounted such that its plane is substantially perpendicular to the longitudinal plane of the shelf support.

14. An apparatus as claimed in claim 14 wherem the shelf is not perpendicular to the plane of the shelf support.

15. An apparatus as claimed in claim 15 wherein the angle formed between the plane of the shelf and the longitudinal plane of the shelf support is less than 90? .

16. An apparatus as claimed in any one of the previous claims further comprising means for generating a vacuum.

17. An apparatus as claimed in claim 16 wherein the means for generating a vacuum comprises a vacuum pump.

18. An apparatus as claimed in any one of claims 8 to 12 wherein the heating means comprises a circulating fluid and/or an electric element.

19. An apparatus as claimed in any one of the preceding claims wherein the chamber wall, shelf and shelf support do not have no exposed bolts, screw threads, crevices, ledges or the like.

20. An apparatus as claimed in any one or more of the preceding claims having a second clo sable door .

21. An apparatus as claimed in claim 21 having a front and rear door to permit access to the chamber from the front and rear.

22. An apparatus as claimed in any one or more of the previous claims having a glove box operatively connected thereto.

23. An apparatus as claimed in claim 22 wherein a glove box is associated with each door of the apparatus.

24. An apparatus as claimed in any one of the previous claims wherein the apparatus comprises a plurality of shelves each supported at its distal ends by a shelf support to form a shelf stack.

25. An apparatus as claimed in claim 24 wherem each shelf stack is removeably mounted to the chamber wall.

26. An apparatus as claimed in claim 25 wherein the shelf stack is removeably mounted at two mounting means.

27. An apparatus as claimed in claim 26 wherein the mounting means are covered by a flange.

28. An apparatus as claimed in any one of the preceding claims wherein the heating fluid supply and return pipes are integrally formed within the shelf support and directly welded to the shelves.

29. An apparatus as claimed in any previous claim for use in freeze drying.

30. An apparatus as claimed in any one of the previous claims for aseptic and/or non-aseptic processing.

31. An apparatus as claimed in any one of the previous claims capable of being sterilised via steaming in place or dry heat sterilisation.

32. An apparatus as claimed in any one of the previous claims having shallow tray depths .

33. An apparatus as claimed in any one of the previous claims being self-draining.

34. An apparatus as claimed in any one of the previous claims wherein the heating fluid supply and return pipes have restriction orifices to ensure uniform flow through each of the heated shelves.

35. A method for drying a wet product cake by evaporating a solvent, comprising the steps of: a) placing said wet product cake within a vessel and placing said vessel upon a support within a vacuum chamber;

b) evacuating said chamber to reduce the pressure within the interior of said chamber to a desired value which accelerates evaporation, but which does not initiate boiling of the solvent; c) supplying heat to said wet product cake without degrading said chemicals at said desired pressure; and

d) supplying a substantial flow of inert gas across the top of said plate.