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Chemical reactor with heat pipe coolingRelated Patent Categories: Chemical Apparatus And Process Disinfecting, Deodorizing, Preserving, Or Sterilizing, Chemical Reactor, Including Heat Exchanger For Reaction Chamber Or Reactants Located ThereinChemical reactor with heat pipe cooling description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050255015, Chemical reactor with heat pipe cooling. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an improved chemical reaction apparatus which is capable of removing large heat fluxes from a viscous reaction mixture while maintaining the reaction mixture at essentially isothermal conditions. The invention also relates to a method of conducting chemical reactions, and in particular, polymerization reactions, at essentially isothermal conditions using the novel reactor of the invention. [0003] 2. Description of Related Art [0004] A variety of commercially important chemical reactions, and in particular polymerization reactions, require that reactants be maintained within a narrow temperature range to achieve desired product properties. [0005] In the case of certain polymerization reactions, due to the low conductivity and high viscosity of the reaction mixture, heat transfer is a limiting factor in reactor design. Further, it is frequently not possible to compensate for the low conductivity of a polymer reaction mixture by using lower coolant temperatures because low coolant temperatures cause polymer solidification in the reactor. In many polymer reactors, the poor heat transfer characteristics of polymer reaction mixture results in poor reaction temperature control resulting in the formation of undesirable products in the reactor. For example, temperature variations in polymer reactors can lead to the formation of polymer products having lower molecular weight than desired. This negatively affects the flow and mechanical properties of the desired polymer end product. Since it is frequently the case that undesirable polymer reaction products are not easily separated from desired polymer products, many attempts have been made to produce polymer reactors which are capable of controlling, within a narrow temperature range, the reaction temperature of highly viscous reactants with poor thermal conductivity. [0006] A wide variety of designs have been developed for continuous flow polymerization reactors which can handle viscous process liquids with poor thermal conductivity. [0007] U.S. Pat. No. 2,727,884 to McDonald describes a polymer reactor which uses forced convection heat transfer. In this reactor, banks of cooling tubes in which a heat transfer fluid is circulated are gently agitated in the polymer reaction mixture. The agitation improves heat transfer, and at the same time preventing channeling of less viscous material in the reactor. Examples of another type of mechanically agitated, convection-type reactor, known as a wiped-film reactor, are disclosed in U.S. Pat. No. 3,513,145 to Crawford, U.S. Pat. No. 3,679,651 to Kii and U.S. Pat. No. 4,011,284 to Gawne. The construction of the internal coils required by such reactors is extremely labor intensive and therefore very costly. Further, the internal heat transfer coils employed in such reactors have a history of failure causing polymer to be contaminated with heat transfer oil. Despite the agitation in these reactors, the heat transfer characteristic of wiped-film reactors is nevertheless poor and hot spots frequently develop in such reactors. [0008] Another example of a polymer reactor designed to provide high heat removal capability is disclosed in U.S. Pat. No. 3,838,139 to Latinen. This patent describes a horizontal cylindrical reactor vessel equipped with an agitator consisting of a plurality of discs with small clearance with respect to the cylindrical vessel. The discs divide the reactor vessel into compartments. The heat of reaction is removed from the reactor by the direct evaporation of a volatile monomer from the reaction mixture. Although this form of heat transfer is generally accepted as more efficient than convection, hot spots with temperature difference as high as 5-10.degree. C. are still experienced. Further, the temperature in the various compartments of the reactor are not necessarily the same due to different polymer concentrations and reaction rates in the compartments. [0009] Using the vaporization of volatile monomer reactants to remove the heat reaction from a polymer reaction mixture is generally not workable when the polymer reaction involves the co-polymerization of more than one monomer. In such cases, the vaporization of the different monomers is generally not equal causing uncontrolled concentration of the different co-monomers. Consequentially, the use of direct evaporation is to be avoided in such cases. [0010] U.S. Pat. No. 4,419,488 to Fukumoto discloses another direct evaporation-type polymerization reactor. The inclusion of a mechanical agitator in a polymer reactor is often an unwanted necessity to improve heat transfer and homogeneity. These devices are costly, require much maintenance and can cause quality problems because the agitator shaft seal is often a source of air ingress to a reactor, which can generate undesirable oxidation by-products such as aldehydes and ketones. These compounds can retard a polymerization reaction and can cause product discoloration. [0011] Several designs have eliminated the use of mechanical agitators in polymer reactors. U.S. Pat. No. 4,421,162 to Tollar and European Patent No. 0150225 A1 describe the use of flat annular plates disposed coaxially within a reactor shell. This concept can be applied to a polymerization reactor with a viscous reaction mixture by causing the heat of reaction to first be absorbed by conduction through the flat annular plates and then by conductive tubes which are in contact with the annular plates and then by convection into an appropriate heat transfer liquid flowing through the conductive tubes. The temperature in such reactor is usually well controlled, however, the volume occupied by the annular plates and tubes in the reactor reduce available reactor volume significantly. Variations of this heat transfer mechanism has been proposed by other inventors such as Oldershaw in U.S. Pat. No. 3,014,702, Brassie in U.S. Pat. No. 3,280,899, Aneja in U.S. Pat. No. 4,808,262 and Mattiussi in U.S. Pat. No. 5,084,134. [0012] Anionic polymerization reactions have also been conducted in continuous stirred tank reactors. However, such reactions must generally proceed at low temperature due to the extreme reactivity of the reactants. Because it is desirable to operate continuous flow reactors hydraulically full to enable simple process control, heat removal in these reactors cannot depend on evaporation. Consequently, such reactors most often rely upon cooling jackets for heat transfer. However, the effectiveness of cooling jackets on anionic polymerization reactors is constrained by the low heat transfer coefficients applying of the convection mechanism and by the limited range of coolant temperature imposed by polymer solidification temperatures. [0013] It would be desirable if there were available a continuous reactor for viscous polymer reaction mixtures with improved heat removal capability and with the capability of maintaining an essentially isothermal temperature profile throughout the reactor regardless of any varying heat loads associated with different reaction rates or reaction products. It would also be desirable if such a reactor were to be easy to construct, operate and maintain. It would further be desirable if the reactor were to have a relatively large void fraction for the conduct of polymerization reactions in as small a vessel as possible. [0014] These benefits and other advantages are achieved with the present invention SUMMARY OF THE INVENTION [0015] A stratified flow reactor of the invention consists of a shell, a heat transfer fluid channel, at least one heat pipe and a plurality of fins. The reaction zone is the shell side of the reactor and the heat pipe or heat pipes with fins mounted thereon extend through the reaction zone. The heat pipe or pipes are in fluid communication with the heat transfer fluid channel. The reactor vessel is closed at one end with at the other end being a cooling chamber through which the heat pipe or multiple heat pipes protrude. The heat pipe or pipes act as super heat conductors from the fins to the heat transfer fluid channel. In a preferred embodiment, the stratified flow react if the invention is a continuous flow polymerization reactor. [0016] As described in U.S. Pat. No. 2,350,348 to Gaugler, heat pipes utilize evaporation of a heat transfer fluid from a porous medium affixed to a heat transfer surface to absorb heat. In the present invention, the heat pipe removes the heat of reaction from the reaction mixture by evaporative cooling from the heat transfer surface of the heat pipe system. The porous medium on the heat transfer surface is commonly referred to as a "wick". The evaporation of the heat transfer fluid from the porous medium or wick enjoys extremely good heat transfer coefficients and enables extremely high heat flux at essentially isothermal conditions. If desired, the evaporated heat transfer fluid is condensed and returned to the heat transfer zone of the reactor. Since heat transfer coefficients associated with condensation are also high, both the heat absorption and heat release segments of the heat pipe equipped reactor of the invention enjoy very high heat flux rates. [0017] The benefits of utilizing a heat pipe heat transfer device in the reactor of the invention as described are derived from its converting what would otherwise be convection heat transfer or submerged heat transfer surface evaporative cooling to evaporative cooling of a thin film from a porous surface from which the evaporated heat transfer fluid can quickly and easily escape. Convection heat transfer is limited by many factors, including the velocity of the heat transfer fluid, the temperature differential between the reaction mixture and the cooling fluid, the viscosity of the heat transfer fluids, the surface area available for heat transfer, the materials of construction of the heat transfer device and the condition of the heat transfer surfaces, i.e., whether they are fouled. Conventional evaporative cooling from a submerged heat transfer surface enjoys higher heat transfer coefficients than convection cooling, but is limited by the liquid phase surrounding the submerged tubes. The heat pipe substitutes thin film evaporation for submerged heat transfer surface boiling with a corresponding improvement of the tube side heat transfer coefficient of up to 10 times. Further, the heat release segment of the reactor of the invention relies upon the condensation of a heat transfer fluid which can take place in a condenser which is remote from the reactor, so that the surface area available for cooling need not be limited to the area of the heat pipe. Accordingly, condenser(s) with sufficient surface area to handle the required heat flux can be located away from the reactor of the invention while still being in close proximity to it. [0018] Because the evaporation of a pure heat transfer fluid occurs at a single temperature and the heat transfer coefficients for the heat pipe heat transfer system of the present invention are very good, a stratified flow reactor equipped with a heat pipe heat exchange device according to the present invention can be operated at essentially isothermal conditions. [0019] As described by Faghri ("Heat Pipe Science and Technology", Taylor and Francis, 1995) and by Peterson ("An Introduction to Heat Pipes", John Wesley & Sons, 1994), the choice of the material of construction, the choice of the heat transfer fluid and the design of the wick structure for the heat pipe apparatus of the invention are within the capability of those skilled in the art. The materials of construction in contact with the heat transfer fluid are commonly selected from copper and copper alloys, aluminum and its alloys and stainless steels. [0020] Although the term heat "pipe" is used in the description of this invention, innumerable configurations are possible, some of which are far from the cylindrical shape of a conventional pipe. For example, possible shapes could be, but are not limited to, flat, rectangular, annular, polygonal or tubular. When tubular heat pipe design is used, tube size can vary from less than 1 mm to several cm in diameter. [0021] The heat pipe heat transfer system of the present invention is comprised of two or three sections: (1) an evaporator section where heat is absorbed by vaporizing a liquid heat transfer fluid, (2) an adiabatic section where the vaporized heat transfer fluid flows without changing state, and optionally, (3) a condenser section where the vaporized heat transfer fluid is condensed using an external source of cooling. The heat transfer fluid condensate can be returned to the evaporator section of the reactor by gravity or by pumping. The evaporator section of the heat pipe heat transfer system of the invention is comprised of a heat transfer tube having a porous surface or wicked internal surface. The heat transfer fluid is supplied to the porous or wicked heat pipe surface where the wicking action of the porous surface or wick wets the heat pipe with a thin film of heat transfer fluid. Because wicking is a surface tension phenomenon which can be limited in long heat pipes by liquid head, it is sometimes preferred for a reactor according to the invention to be comprised of multi-reactor sections, each having heat pipe transfer zones. [0022] The heat pipe of the invention may be 1) sealed or 2) of the thermosyphon type. Continue reading about Chemical reactor with heat pipe cooling... Full patent description for Chemical reactor with heat pipe cooling Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Chemical reactor with heat pipe cooling patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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