Abstract:
An improved closure device for a laboratory scale chemical reactor which provides fast and efficient opening and closing of the reaction vessel as well as providing a simple and reliable system for relieving excessive pressure should it build up in the reaction vessel. The reactor is sealed by use of a substantially flat head that is seated against the rim of the reaction vessel by pressure which is generated by a variably adjustable closure means. Since the closure pressure can be adjusted to any value within the design limitations of the closure means, the closure means also operates as a pressure relief valve.

Description:
[0001]    The present invention relates to reactors and methods for the synthesis of chemical compounds. Specifically, it relates to closure mechanisms for these reactors which permit the fast and efficient opening and closing of the reaction vessel. In addition, the present invention relates to a simple and reliable system for relieving excessive pressure should it build up in the reaction vessel.  
         BACKGROUND OF THE INVENTION  
         [0002]    Reactors are used to synthesize various chemical products, such as polymers, from starting materials, commonly referred to as reactants. Industrial or full scale reactors subject these chemical reactants to certain, often unknown or unanticipated, chemical and physical conditions that are difficult if not impossible to imitate in small scale reactors used in laboratories. The synthesis chemist needs to know how a certain reaction might occur at the molecular level in an industrial sized reactor. Laboratory scale reactors perform this necessary service.  
           [0003]    Certain laboratory scale equipment, such as reactor kettles, are universally used to create polymers. Traditionally, reactor kettles are spherically shaped and are made of glass. They have a plurality of openings or ports located on, when the reactor kettle is installed in its mounting bracket, its top side. These ports are used to hold in place tubes, usually sealed with stoppers, which are made out of either rubber or other substances that will not react with the material in the kettle. Chemical reactants may be delivered to the inside of the reactor kettle through feed tubes in the stoppers. Another port may house a thermometer or other sensing devices. Also, one of these ports will house the shaft of an agitator.  
           [0004]    The problem with having to insert the agitator through the opening of the common reactor kettle port is that because of the narrow diameter of the port, only a very limited variety of agitator blade designs can be utilized. The most common agitator which can be used in reactor kettles consists of a blade which is loosely secured to the agitator by a pinion-type securing means. During insertion through the narrow diameter port, the blade must be aligned parallel to the agitator shaft. Then, once inside the reactor kettle, the operator must manipulate the agitator so that the blade rotates ninety degrees to the stirring shaft. This is a very labor intensive and time consuming operation and may require many attempts before the blade becomes oriented in the proper alignment to perform its intended function. These constraints limit the variety of blades which might otherwise be used to stir the reactants. As if the insertion process wasn&#39;t difficult enough, at the completion of the synthesis reaction, the agitator blade must then be oriented parallel to the agitator shaft so that the entire agitator can be removed from the reactor kettle for cleaning. The manipulation required to perform this process may be more time consuming, not to mention more frustrating for the operator, than the process of inserting the agitator blade into the reactor kettle in the first place.  
           [0005]    Initial solutions to the problems presented by these substantially spherical, glass reactor kettles involved the design of a substantially cylindrical resin kettle having a large opening at the top, essentially of the same diameter as the internal reaction vessel. The reaction vessel is sealed by a cover or lid. These resin kettles may be jacketed, having one or more shells surrounding, but spaced apart from, the internal wall of the reaction vessel. The space between the shell and the vessel wall may be filled with circulating gas or liquid for cooling and/or heating purposes.  
           [0006]    In certain industries, such as the food and pharmaceutical industries, cleanliness and the ability to continuously maintain the cleanliness of the resin kettle are critical. Even for many industrial applications, cleanliness is of the utmost importance where even the slightest amount of contamination may interfere with a reaction process. The inner surfaces of the reaction vessel are often coated with glass or other non-metallic, corrosion and/or temperature resistant material. Many of these materials, such as glass, tend to be relatively brittle and are prone to fracture upon impact or significant distortion.  
           [0007]    The use of a reaction kettle with a lid as described above created other problems. In order to attach heads, covers, tops, fixtures, piping, etc. to these resin kettles, it is necessary to employ specialized joints which will substantially reduce the risk of harming these fragile coatings. These joints are designed to generally uniformly distribute stress, whether at ambient or elevated temperatures. The problems with simply adding joints to devices that perform chemical processes at elevated temperatures and under super-atmospheric pressure is that contaminants readily accumulate at such joints.  
           [0008]    Traditional designs of such joints include two opposing, substantially parallel rigid surfaces having a gasket and/or other deformable material between them. In order to provide a sealed environment, a plurality of clamps or securing means are arranged around the perimeter of the lid to secure it to the reaction vessel. The structure which supports the securing means must be rigid enough to uniformly distribute a force, without distorting the joint surfaces, to effect the uniform compression of the gasket material in order to seal the two opposing surfaces. This force must be substantial enough to withstand the high internal pressures, and at elevated temperatures in some cases, that might be generated within the reaction vessel. Alternatively, the resin kettle may be used to conduct a reaction at ambient or even cryogenic temperatures and/or under sub-atmospheric.  
           [0009]    The securing means of these resin kettles may be permanently, but movably, attached to either the lid or around the top rim of the vessel wall. Alternatively, they may be entirely separate and distinct from the joints formed between the abutting flanges. The time intensive task of removing or installing the lid or head is determined somewhat by the need to uniformly apply or relieve the pressure around the annular shaped abutting flanges. Traditional designs of securing means include exposed screw mechanisms, or over-riding cam mechanisms, all of which have multiple crevices, corners and pockets in which contaminants might build up. Contamination poses a significant problem which requires a great deal of time for cleaning.  
           [0010]    Solutions to these problems are suggested in EP 0462383 B1 which discloses a chemical reactor vessel in which the securing means is not prone to contamination by the reactants in the vessel. A flange integral with the top rim of the reaction vessel is interposed between the securing means and the contents of the reactor so as to reduce the chances of contaminants accumulating at the securing means. However, while this disclosure might offer a seemingly more efficient system for maintaining the cleanliness of a laboratory resin kettle, it still utilizes one of the traditional systems for securing the lid to the reactor vessel, a screw mechanism. The opening and closing of the resin kettle described in this disclosure is still a very time consuming process.  
           [0011]    Further, resin kettles using screw or cam type sealing mechanisms present an additional problem. Because the head or top portion of the resin kettle must be repositioned on the reactor vessel every time it is closed by the operator, it is difficult to insure that the head is positioned in the precise position for which it was designed in order to effect the best possible seal, even if the head is somehow hinged.  
           [0012]    Another problem that must be addressed in the use of laboratory scale reactors is that of the need to relieve pressure if reaction conditions produce an excessive amount of pressure. Traditional means for relieving internal pressures comprise the use of one or more pressure relief valves, such as is shown in U.S. Pat. No. 4,682,622. Adding another device, such as a pressure relief valve located either on the reactor itself or to connecting pressure tubing connected to the resin kettle, adds to the complexity of the entire system. The pressure control valves are usually threaded into the wall of the reactor, or to a specially fitted plug. Due to different coefficients of expansion for the threaded portion of the pressure control valve and for the resin kettle or its threaded insert will contribute, over time, to the aggregation of contaminants. This, in turn, can cause the entire pressure control valve to become clogged be forcefully expelled from the reactor at an undetermined pressure. This uncertainty of reliable operation of the pressure control valve cannot insure the chemical integrity of the end product. Further, should the pressure relief valve become completely clogged by contaminants so as to render it useless for its intended function, it would probably fail to operate under super-atmospheric conditions, thereby increasing the risk of an explosive relief of pressure. What is needed therefore, is a closure and sealing mechanism for a laboratory scale chemical reactor that significantly improves productivity by enabling the rapid closure and opening of the reactor vessel, permits interchangeability between the reactor vessel and the head and eliminates the excessive building up of contaminants in the working parts and on the sealing interfaces of the reactor. In addition, what is needed is a simplified and more reliable pressure relief device. As shown below, the laboratory scale closure mechanism of the instant invention presents a novel solution to these problems.  
         STATEMENT OF THE INVENTION  
         [0013]    In a first aspect, the chemical reactor closure mechanism of the present invention consists of a reaction vessel, having a rim at the top, a separable head, wherein the head is slideably connected to at least one vertically disposed guide shaft which permits the head to move only in a vertical direction; and, a closure means operatively connected to the head, wherein the closure means comprises  
           [0014]    a drive cylinder,  
           [0015]    a pressure source selected from either pneumatic or hydraulic systems, and  
           [0016]    a pressure control means to regulate the amount of force exerted by the closure means to securely seal the head to the rim.  
           [0017]    In a second aspect, the head functions as a pressure relief means.  
           [0018]    In a third aspect, there is provided an improved method for sealing a laboratory scale chemical reactor, wherein the reactor comprises a reaction vessel having a rim at the top, a head having an inner surface positioned to face the interior of the reaction vessel, and a closure means, wherein a variable amount of force that is delivered by either a pneumatic or hydraulic pressure system is exerted on the head by the closure means. The force is infinitely adjustable within the pressure capabilities of the components of the closure means. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0019]    In order to better show the present invention, the following drawings are provided. They are not intended to limit the scope of the invention to what is exemplified herein.  
         [0020]    [0020]FIG. 1 is a semi-schematic, cross-sectional side elevational view of the laboratory scale reactor, showing the head in the closed position.  
         [0021]    [0021]FIG. 2 is semi-schematic, cross-sectional side elevational view of the laboratory scale reactor, showing the head in the open position.  
         [0022]    [0022]FIG. 3 is a semi-schematic, cross-sectional view of a portion of the laboratory scale reactor, showing a magnified image of the seal formed between the rim of the vessel and the head.  
         [0023]    [0023]FIG. 4 is a semi-schematic, top elevational view of the laboratory scale reactor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    The laboratory reactor  10  of the present invention consists of a reaction vessel  12 , having an inner surface  14  and an outer surface  16 . The circumferential rim  13  at the top of the reaction vessel  12  defines an opening through which reactants are added to and reaction products removed from the interior  22  of the reaction vessel  12 . Positioned above and, during the processing of reactions, in contact with the rim  13  is the head  18 . The head  18  is comprised of a substantially flat, rigid material capable of withstanding the compressive force necessary to seal the interior  22  of the reaction vessel  12  during chemical reactions without being deformed or fracturing. Suitable materials include cast steel, stainless steel, titanium and engineered polymeric resins, which may or may not be filled with glass or carbon particles.  
         [0025]    The head  18  comprises two opposing surfaces, an interior head surface  20 , which faces the interior  22  of the reaction vessel  12  and an exterior head surface  21 . In order to provide an effective seal between the rim  13  and the interior head surface  20 , it is necessary to add a deformable seal  23 . The seal  23  may consist of any deformable material capable of effecting a tight seal, such as an O-ring. Preferred materials are elastomeric polymers. Further, in order to protect elastomeric polymers from chemical attack caused by contact with the reactants, an inert material, such as Pertetrafluoroethylene (PTFE), may be employed to coat the surface of the seal  23 . The seal  23  sits in an annular channel  25  that is cut into or formed on the surface of rim  13  that faces the head  18 . The annular channel  25  keeps seal  23  from moving and insures that when seal  23  begins to deform under the pressure exerted by the closing of the head  18  on the reaction vessel  12 , the seal  23  maintains its position.  
         [0026]    Chemical reactants  24 , either in liquid, solid or gaseous form, may be added to the interior  22  of the reaction vessel  12  either all at once or sequentially, if required, as the reaction progresses. If the reactants are added prior to initiating the reaction, they may be placed into the interior of the vessel  22  while the head is removed. If, however, some of the reactants need to be added sequentially while the reaction is progressing, one or more feed tubes  38  may be positioned in the head  18 . The feed tube  38  has an inlet  39  and an outlet  40 , the outlet  40  projecting through the interior head surface  20  in order to deposit the sequentially fed reactants into the reactants  24  already present in the interior space  22  of the vessel  12 . The feed tube  38  will be fitted with a means to seal off the feed tube when not in use so as to prevent releasing reactants or relieving pressure from the reaction vessel  12 .  
         [0027]    An agitator assembly  26  is used to provide mixing for the reactants  24 . The portion of this assembly disposed in the interior  22  of the vessel  12  consists of an agitator output shaft  28  and an impeller  30 . The output shaft  28  is sealably routed through a hole in the head  18  and is connected at its upper, or input end, to an agitator drive means  32 . The agitator drive means may comprise any power source capable of providing rotational energy to the output shaft  28 . However, an electric motor is considered most suitable. The agitator drive means  32  is supported above and in proximity to the exterior head surface  21  by an agitator mounting bracket  34 .  
         [0028]    Sensor  42  may be added to detect a variety of chemical and physical properties of the reactants  24  during the reaction process. Sensor  42  comprises a sensor shaft  44  which descends from the interior head surface  20  into the interior space  22  of the reaction vessel  12 . At the end of the sensor shaft  44  which is located in the reaction vessel  12 , is at least one detector  46 . Of course, since it is desirable to monitor multiple characteristics of the reactants  24  during the reaction process, such as temperature, pH, various levels of certain ions, etc., a plurality of different detectors may be located at the end of the sensor shaft  44 . The sensor shaft  44  is connected to a relay  50  which is removably secured to the head  18  by a sensor mounting bracket  48 . Relay  50  compiles the raw data acquired from the plurality of detectors  46  and transmits it to a data processing and data storage device, such as a computer (not shown in the Drawings).  
         [0029]    The vessel  12  is securely positioned by a reactor support bracket  51 , which is, in turn, securely attached to a support base  52 , generally referred to as the vessel assembly  53 . This provides the reaction vessel  12  with the structural support needed during the processing of reactions or if detached from the rest of the components of the laboratory reactor  10 . Support base  52  is releasably secured to conventional guide rails  69  and  69 ′ to insure accurate positioning of the support base  52  to head assembly  55 . Head assembly  55  comprises the support structure for the head  18 , and consists of substantially rigid material, such as steel or engineered resins. Optionally, a locking means, such as threaded or cam actuated devices may be employed to securely interlock head assembly  55  and vessel assembly  53 . Since the guide rails  69  and  69 ′ insures the repeatability of the accurate alignment of the reaction vessel  12  and the head  18 , multiple copies of the vessel assembly  53  can be produced for interchangeable use with a single head assembly  55 . This vastly improves the speed of doing multiple reactions with the same head assembly  55 .  
         [0030]    In order to seal the laboratory reactor  10  during the reaction process, interior surface  20  of the head  18  is forcibly pressed against the top surface of rim  13  of the reaction vessel  12 . At least one closure means  54  (two closure means are showed in FIG. 1 and FIG. 2, with the second one identified by the prime symbol) provides the pressure required to produce an effective seal. Closure means  54  comprises a drive cylinder  57  which is securely fastened to the base of the head assembly  55  by drive cylinder support shaft  59 . Drive cylinder  57  is securely attached to head  18 . The design exemplified by the Figures shows only one orientation of closure means  54 . Another orientation, equally preferable, is for drive cylinder  57  to be securely attached to the base of head assembly  55  and for the drive cylinder support shaft  59  to be securely attached to the head  18 . Securely attached to each end of drive cylinder  57  a pressure line or hose  56 . The closure means shown in FIGS. 1 and 2 is intended to be exemplary. Any suitable hydraulic or pneumatic pressure cylinder design may be utilized. The underlying element is that the closure mechanism be attached to the head so as to separate it vertically from the reaction vessel, on the one hand, and be able to exert the pressure necessary to provide a seal between the head  18  and the top of the rim  13 , on the other.  
         [0031]    Hose  56  is shown in two segments,  56   a , which is connected to the lower end of the drive cylinder  57  and  56   b , which is connected to the top end of drive cylinder  57 . Based on the exemplified design, in order to close the laboratory reactor  10 , pressure is delivered from an external pressure source (not shown) and is routed via pressure line  68 , through pressure control valve  60  and distributor  58 , then through hose  56   b  to drive cylinder  57  to exert a downward force on the head  18 . The interface between the interior surface  20  of head  18  and the top of rim  13  thus forms a secure seal by compression of seal  23 . When it is desired to open the laboratory reactor  10 , pressure from the distributor  58  will be routed through hose  56   a , which then releases the pressure on the seal  23  and vertically raises the head  18 . The use of pneumatic or hydraulic pressure systems provides that substantially an infinite number of pressure values may be selected by the closure means  54 , limited only by the design limitations of the components of the laboratory scale reactor  10 .  
         [0032]    Closure means  54  provides the necessary energy to move the head  18  either up or down. In order to insure that the head  18  is placed precisely at the same location on the rim  13 , guide shafts  63  and  65  are used. These guide shafts  63  and  65  are securely attached to the base of the head assembly  53 . Each are slideably engaged with the head  18  to permit only the vertical movement of the head  18 .  
         [0033]    By having the capability to adjust the amount of pressure which holds the head and reaction vessel together, the closure means  54  is able to perform the function of a pressure relief valve. The reactor operator may adjust the pressure exerted by the closure means  54  to a predetermined constant amount, sufficient to hold the head  18  in its closed position on the rim  13  of the reaction vessel  12 . Any pressure that might build up in the reaction vessel  12  that generates a force higher than the force which securely engages the head  18  to the reaction vessel  12  during processing will cause the seal to rupture, thereby relieving the buildup of pressure in the reactor. This is desirable to having excessive pressure build up in the reaction vessel  12  and risking the possibility of an explosion.  
         [0034]    Having disclosed the advantages of the improved laboratory chemical reactor closure mechanism, the following now sets forth the boundaries of the claimed subject matter.