Patent Application
20090110599
The invention is concerned with new methods of operating surface reactors, and with new reactors employing such methods, and especially to methods and reactors employing gas-shearing of reactant films to facilitate reaction between the reactants.
Frequently it is necessary to change the chemical or bio-chemical reactants employed in the synthesis of active pharmaceutical ingredients (APIs) or intermediates. These usually comprise small molecules or molecular building blocks which subsequently are used in the production of the required pharmaceutical compound. Such reactions usually involve the use of very expensive reagents, solvents and catalysts, which are reacted in batch reactors of minimal volume to keep the production costs at a minimum. Typically, one or even less than one milliliter of each reagent is employed, the reagents being simply added together in a small enough single vessel or a plurality of vessels, the contents of which are then subjected to some form of agitation by shaking, swirling or similar periodic motion to improve the very slow process of natural molecular interdiffusion, which is required to bring about the desired synthesis. Completion of such reactions may take several minutes but most frequently several hours. The development of a new pharmaceutical compound may require many hundreds, or even thousands, of such small volume reactions as the structure of a promising molecule is “tweaked” to achieve maximum efficacy with minimum undesirable side effects, and any improvement in yield with or without reduction in reaction time is most welcome to the industry.
It is an object of this invention to provide new methods of operating reactors and reactors employing such methods which facilitate fast and high rate conversion chemical reactions involving liquid-liquid, solute-liquid, liquid-solid, solute-solid, liquid-gas and solute-gas reactions.
In accordance with the invention there is provided a method of operating a reactor to react together at least two reactants, at least one of which is in liquid state, the reactor being of the type comprising:
a rotor mounted for rotation about a longitudinal axis and having a cylindrical exterior surface disposed about the axis;
motor means connected to the rotor and operative to rotate it about the axis;
a stator enclosing the rotor and having a cylindrical interior surface disposed about the axis parallel and coaxial with the rotor exterior surface to provide between the two surfaces a reaction chamber of transverse annular cross section, preferably of uniform radial thickness along its length;
means for introducing reactants to be reacted together into the reaction chamber; and means for discharging reacted reactants from the reaction chamber;
the method including the steps of:
providing within the reaction chamber a shear transmitting fluid in gaseous state capable of transmitting shear force applied thereto by the moving rotor exterior surface to the stator interior surface;
feeding into the reaction chamber a quantity of the reactants with rotation of the rotor at least at a speed sufficient to spread the reactants under the urge of the shear transmitting fluid under centrifugal force over the stator interior surface as a reactant film of radial thickness 150 micrometers or less, preferably 120 micrometers or less, and more preferably 100 micrometers or less; and
simultaneously or subsequently rotating the rotor at a speed such as to apply to the reactant film via the shear transmitting fluid a shear force sufficient to disrupt molecular clusters therein and thereby facilitate molecular diffusion reaction between the reactants.
Also in accordance with the invention there is provided reactor apparatus for reacting together at least two reactants, at least one of which is in liquid state, the reactor being of the type comprising:
a rotor mounted for rotation about a longitudinal axis and having a cylindrical exterior surface disposed about the axis;
motor means connected to the rotor and operative to rotate it about the axis; a stator enclosing the rotor and having a cylindrical interior surface disposed about the axis parallel and coaxial with the rotor exterior surface to provide between the two surfaces a reaction chamber of transverse annular cross section, preferably of uniform radial thickness along its length;
means for introducing reactants to be reacted together into the reaction chamber; and
means for discharging reacted reactants from the reaction chamber;
wherein the radial dimension of the reaction chamber is not less than 1 mm;
the reaction chamber has therein a shear transmitting fluid in gaseous state capable of transmitting shear force applied thereto by the moving rotor exterior surface to the stator interior surface;
the means for introducing reactants into the reaction chamber is adapted to feed therein a quantity of the reactants with rotation of the rotor at least at a speed sufficient to spread the reactants under the urge of the shear transmitting fluid under centrifugal force over the stator interior surface as a reactant film of radial thickness not more than 150 micrometers;
and the rotor is capable of rotation at a speed such as to apply to the reactant film via the shear transmitting fluid a shear force sufficient to disrupt molecular clusters therein and thereby facilitate molecular diffusion reaction between the reactants.
The area of the stator interior surface may be such that a total of 2 ml of reagents will result in a reactant film on the stator interior surface of thickness 150 micrometers or less. The radial dimension of the reaction chamber may be between 5 mm and 500 mm, and preferably is at least 3 mm. Unwanted vapors and gases generated during the reaction may be removed from the reaction chamber.
The shear transmitting fluid may be air, a reactant gas or an inert gas. The rotor may be rotated at speeds between 30,000 and 80,000 r.p.m., and the consequent shear rate obtained in the reacting film may be between 150,000/sec and 800,000/sec.
The reactor may comprise sampling means for removing samples from the reacting film for determining the stage which the reaction has reached. The reactor may comprise a detector able to examine the film to determine the stage which the reaction has reached.
At least one reactant is in gaseous state and is entrained in the shear transmission fluid. Pressurized gas is introduced into the reaction chamber to purge liquid reagents and reacted reagents from the reaction chamber adhering to the stator interior surface.
Methods and apparatus that are particular preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein:
The apparatus comprises a base member 10 on which is mounted a cylindrical base tube 12 with its side wall struck about a vertical axis 14, a part of the wall provided having an opening (not shown) through which a beaker 16, or any equivalent vessel, may be inserted into and removed from a chamber 17 within the tube interior. An annular cap 18 having a central opening 20 centered on the axis 14 is mounted on the top end of the cylinder 12 and in turn supports a cylindrical stator tube 22, also having its wall struck about the axis 14. The top end of the tube 22 is closed by a cover plate 24, which also has a central opening 26 centered on the axis 14, the assembly of base plate 10, cylinders 12 and 22, cap 18 and cover plate 24 being held rigidly together by a plurality of circumferentially disposed longitudinal tie rods 26 (only one shown) and butterfly nuts 28. A high speed direct drive motor 30 is mounted above the assembly by a gantry arm 32 attached to a vertical post 34 (see
The reaction chamber 44 is filled with a shear transmitting fluid, which in this embodiment can be air or, if air is likely to interfere with the reaction, a more inert gas such as nitrogen or argon. As the rotor spins its external surface 40, it applies rotational shear to the shear transmitting fluid, which is dragged circumferentially in the reaction chamber and in turn applies rotational shear to the stator internal surface 42. First and second reactants to be reacted together are fed into the reaction chamber under precise control as to flow via respective precision metering injectors 52, in this embodiment comprising 1 ml capacity injection syringes, disposed radially opposite to one another. This injection takes place while the rotor is rotated at a predetermined speed and the shear applied by the shear transmitting fluid immediately spreading the reactants over the stator internal surface 42 in the form of a thin film 54 (
It has been found that the thickness of the film formed on the stator wall and subjected to the shear by the shear transmitting fluid is critical for successful facilitation of the required molecular interdiffusion reaction, and a practical upper limit of the thickness is about 150 micrometers. It has been found advantageous to reduce the thickness to a lower value of 120 micrometers, and preferably as low as 100 micrometers. The capacity of a reactor of specific size does of course decrease with decrease in the film thickness, but this is immaterial with many reactions required for the production of APIs, since the quantities involved are already extremely small e.g. 2 ml or less. The use of a gaseous fluid as a shear transmitting medium gives a required flexibility as to the radial dimension required for the reaction chamber 44 and this can be as much as 100-500 mm. Thus, any attempt to produce a reaction apparatus with a rotor and stator forming a reaction chamber with a radial spacing between the cooperating surfaces of the required film dimensions encounters considerable design and manufacturing problems, the most difficult of which to solve are dimensional changes at the high speeds of rotation required and inevitable temperature changes caused by the reaction itself and frictional drag of the reagents against the relatively moving surfaces. All of these problems are solved simply and elegantly by the methods and apparatus of the invention. A specific embodiment of apparatus intended for use with reactions involving approximately 2 ml or less of total reagent volume employs a stator with an internal surface 40 of 5 cm (2 inch) diameter and of 5 cm (2 inch) axial length, while the rotor external diameter is 4.75 cm (1.9 inch) to give a radial dimension for the reaction passage of 0.125 cm (0.05 inch). By contrast the desired maximum thickness of the reagent film 54 is 0.015 cm, and preferably 0.012 cm or less.
Many different permutations of reactants may be employed as long as at least one of them is in liquid state to permit the formation of the required liquid film on the stator inner wall. For example, one may be a solid material in highly divided form that is injected as a powder or a slurry. Again, one may be in gaseous or vapor state that is introduced into the shear transmitting fluid. Many reactions will result in the production of vapors and gases that need to be removed to avoid undesired side reactions or to influence the chemical equilibrium of a reaction and this is done by the provision of a shroud 56 (
After the required reaction time, which can be from less than one second to several minutes, the rotor is stopped abruptly resulting in the draining of the reacted reactants by gravity into the beaker 16 (see
It is vitally important in designing processes for the interaction of fluids, and in designing apparatus wherein such processes are to take place, to understand as fully as possible the “mechanics” of the interactions, and this becomes even more important when such interactions are chemical reactions that will result in new products. The following is presented as an abbreviated version of my understanding to date of the mechanics of such interactions, although I do not intend the scope of the invention to be limited in any way by this presentation. A more detailed presentation will be found in my prior U.S. application Ser. No. 10/656,627 (Publication No. 20050053532A1 of Mar. 10, 2005) the disclosure of which is incorporated herein by this reference. It is believed that achievement of fast inter-diffusion is hampered significantly in all chemical reactions by the diffusion retarding preponderance of what have been referred to by a number of different two word terms, the first of which is “molecular” or “cybotactic” and the second of which is “clusters”, or “swarms” or “domains”. Another term sometimes used is pseudo-compounds. For convenience I have adopted the term “molecular clusters” as my preferred reference to these, unless quoting from some pertinent publication. These molecular clusters inherently occur in liquids below their boiling points, within which clusters the molecules are anisotropically ordered from a kinematics point of view. Such ordering impedes rapid, natural interdiffusion due to the highly coupled oscillation mode of the molecules within the clusters, consisting of large numbers of molecules oscillating in unison and unidirectionally on a cluster scale <100 nm. The problem that arises is to find some way in which practically and economically these molecular clusters can be broken up or sufficiently disturbed so as to greatly facilitate un-clustered, individual reactant molecules to encounter each other on a one on one basis and thereby permitting very rapid and efficient reactions to take place. The present invention provides such a solution.
10. Apparatus base
12. Base cylinder
14. Apparatus and rotor axis
16. Beaker receiving reacted reagents
17. Chamber in base cylinder 12
18. Annular cap
20. Central opening in annular cap 18
22. Cylindrical stator tube
24. Cover plate for tube 22
26. Tie rods holding assembly together
28. Butterfly nuts on tie rods 26
30. Direct drive motor
32. Gantry arm supporting motor
34. Vertical post supporting gantry arm
36. Motor shaft
38. Cylindrical rotor on motor shaft
40. Rotor external cylindrical surface
42. Stator internal cylindrical surface
44. Reaction chamber between surfaces 40 and 42
46. Heat exchange jacket about stator cylinder tube 22
48. Inlet to heat exchange jacket
50. Outlet from heat exchange jacket
52. Precision metering injectors
54. Reactant film
56. Shroud for vapor/gas removal and insertion
58. Sampling septum
60. Sampling pipette
