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
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.
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.
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'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.
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.
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.
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.
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.
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.
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.
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.
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
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
a drive cylinder,
a pressure source selected from either pneumatic or hydraulic systems, and
a pressure control means to regulate the amount of force exerted by the closure means to securely seal the head to the rim.
In a second aspect, the head functions as a pressure relief means.
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.