Abstract:
A reservoir for one or more chemical reactants has means for heating the reactants and optional means for stirring the reactants. A pumped reactant feed line and a return line provide fluid communication between the reservoir and a 4-way valve system. The 4-way valve system is also in fluid communication with a reactor vessel and a source of inert gas for purging the system. In a first state, the 4-way valve provides fluid communication between the reservoir and the reactor. In a second state, the 4-way valve provides a continuous circulation path for the heated reactants from the reservoir, to the valve system, and back to the reservoir via the return line. In a third state, the 4-way valve provides a fluid pathway for purging the reactor with inert gas. In a fourth state, the 4-way valve provides a fluid pathway for purging the reservoir with inert gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS: 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/894,264 filed on Oct. 22, 2013. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention. 
         [0004]    The present invention generally relates to the transportation of heated reagents to a chemical reactor. More particularly, it relates to the transportation of heated reagents in the synthesis of nano-particle-based materials. 
         [0005]    2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98. 
         [0006]    Quantum dots (QDs) consist of tiny particles (nanoparticles) of semiconductor material with dimensions on the order from 2 to 50 nanometers. Because of their size these particles have unique electrical properties, one of which is the emission of visible light under excitation. The color of the light emitted is dependent upon the size of the QD particle. By precisely controlling the size of the particles during manufacture, the color of the light emitted may also be precisely controlled, making quantum dots useful in commercial applications such as optical and electronic devices and other applications ranging from biological labelling, photovoltaics, catalysis, biological imaging, LEDs, general space lighting, and electroluminescent displays amongst many new and emerging applications. 
         [0007]    A method of QD manufacture involves producing nanoparticles from chemical precursors in the presence of a molecular cluster compound under conditions whereby the molecular cluster acts as a prefabricated seed template for the formation of a core semiconductor material. One or more semiconductor shell layers may be grown on the core material. See, for example, U.S. Pat. No. 8,524,365 the entirety of which is hereby incorporated by reference. 
         [0008]    As shown in the system of  FIG. 1 , during QD manufacture, reactants in a reservoir  110  may be added to a reactor  100  by use of a pump  120 . The reaction (or individual reactants) may be sensitive to the presence of oxygen in the system, and an inert gas such as nitrogen, for example, may be used to purge the system. The inert gas may be introduced to the system via a purge line  140  and opening a gas source valve  130 . Reactants may be in the form of a slurry. In some cases, heating the slurry may cause it to form a solution, in whole or in part. Heating a slurry of reactants may make the slurry more uniform prior to its addition to a reactor. 
         [0009]    Line jacketing is commonly used to maintain the temperature of a liquid or slurry within such delivery systems. In these systems the jacket typically contains an electrical heating element to warm the liquid or slurry by electrical conduction via the pipe or the jacket, for example, using heating tape or heating cable. 
         [0010]    Delivery lines may be made of a transparent material such as glass to allow viewing of the reactants and observation and detection of blockages, for example. However, jacketed heating means may obstruct the view of the transparent lines, and prevent an operator from seeing if and where a blockage might occur. Thus, a method to heat the slurry within the lines and without obscuring the view of the flow through the system is needed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    A reservoir for one or more chemical reactants has means for heating the reactants and optional means for stirring the reactants. A pumped reactant feed line and a return line provide fluid communication between the reservoir and a 4-way valve system. The 4-way valve system is also in fluid communication with a reactor vessel and a source of inert gas for purging the system. 
         [0012]    In a first state, the 4-way valve provides fluid communication between the reservoir and the reactor. In a second state, the 4-way valve provides a continuous circulation path for the heated reactants from the reservoir, to the valve system, and back to the reservoir via the return line. In a third state, the 4-way valve provides a fluid pathway for purging the reactor with inert gas. In a fourth state, the 4-way valve provides a fluid pathway for purging the reservoir with inert gas. 
         [0013]    Actuation of the 4-way valve, the pump, heating means, and stirring means may be manually controlled, timer controlled or automatically controlled in response to various temperature, pressure, flow and/or mass sensors. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0014]      FIG. 1  is a schematic diagram of a method of delivering a heated slurry to a chemical reactor in accordance with the prior art. 
           [0015]      FIG. 2A  is a schematic diagram of an embodiment of the invention operating in an addition mode. 
           [0016]      FIG. 2B  is a schematic diagram of an embodiment of the invention operating in a circulation mode. 
           [0017]      FIG. 2C  is a schematic diagram of alternative embodiments of the invention. 
           [0018]      FIG. 3  is a flow diagram of an embodiment of the disclosed system that uses a scale. 
           [0019]      FIG. 4  is a flow diagram of an embodiment of the disclosed system that uses pump timing to deliver a desired quantity of reagents. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    An apparatus and method to transport and warm a fluid such as a slurry without the use of jacketing is disclosed. The apparatus may include a four-way, two-valve system to flow the fluid through the system. Upon passing through the valves, the fluid may either be transferred to a set of return lines that are connected to a heating system in a circulation mode, or flow the fluid through the addition system of lines in an addition mode and depositing the fluid in a reactor. 
         [0021]      FIG. 2A  shows an embodiment of the delivery system  200  in addition mode. Here, fluids (slurries or liquids) are transported from a reservoir  250  through a valve system  210  and added into a reactor  100 . The amount of fluid added to the reactor  100  may be controlled by timing the activation of a pump  120  that may be used to produce fluid flow. The pump  120  may be any positive displacement pump such as a peristaltic pump or a diaphragm pump to assist in maintaining a closed system. Other methods, discussed further below, may also be used to control the quantity of fluid added to the reactor  100 . 
         [0022]    The valve system  210  may be a four-way valve system comprising two three-port valves  215 ,  218  having a port in common. Valves  215 ,  218  may each have an A and B position as shown. The valves may be manually engaged, but are preferably controlled via an automated control system (not shown). To configure the valves in addition mode, valve  215  may be placed in the A position and valve  218  may be placed in the B position. 
         [0023]    The delivery system  200  may have an additional purge line  230  which may be used to purge the reactor, for example, prior to any additions when both valves are set to position B. The delivery system  200  may be purged by introducing an inert gas to the purge lines  140  and  230 , and by the control of valve  215  and valve  218 . The system may be purged by providing positive pressure of the inert purging gas and cycling the valve system  210 . Alternatively, valve  215  may be set to position B and valve  218  set to position A and inert gas from purge line  230  may be routed to reservoir  250  via return line  220 . In such case, reservoir  250  would be equipped with a vent (not shown). 
         [0024]    To keep the fluid warm, the fluid may be circulated through the heating system.  FIG. 2B  shows the delivery system  200  in circulation mode. In circulation mode, valve  215  and valve  218  are both in the A position. This directs the flow of the fluid through a return line  220  to the heating system. The heating system may comprise a reservoir  250  and a heating element  260 . The reservoir  250  may be any vessel known in the art. For example, reservoir  250  may be a clear glass vessel such as a modified conical flask, for example, configured so that the delivery fluid may pass into and out of the reservoir  250  without exposure to oxygen and/or moisture, i.e., a closed system. The reservoir  250  may be fitted with a magnetic stirrer bar, and positioned on top of a heating element  260  such as a stirrer hot plate, for example. The stirring rate and temperature of heating element  260  may be selected to achieve values appropriate for the chosen fluid. 
         [0025]    In one embodiment, the fluid temperature may be controlled manually via heating element  260 . As the fluid passes from return line  220  into reservoir  250 , it may be heated and stirred (to ensure uniform heating, for example). As the fluid continues to flow into reservoir  250 , the warmed delivery fluid in reservoir  250  may be circulated back into supply line  160 , towards four-way valve system  210 . The inlet of the supply line  160  may be positioned at or near the bottom of reservoir  250  to ensure that supply line  160  receives fluid that has been warmed and mixed. On reaching four-way valve system  210 , the delivery fluid may be directed through to the addition system or back through the heating system. 
         [0026]    The state of valve system  210 , heating element  260 , stirring rate, and pump  120  may be controlled by a timer and/or controlled by an automated control system, for example, a processor-based system. Further, the automated control system may take input measurements at various places in the delivery system  205  as shown in  FIG. 2C .  FIG. 2C  shows delivery system  205  which includes other configurations of the system  200 . Namely, scale  270 , heat exchanger  280 , and various measurement points  290  may be added to delivery system  200 . Alternatively, as illustrated in  FIG. 2A , the temperature may be controlled by an automatic system utilizing a thermocouple  252  or other temperature-sensing means immersed in the contents of reservoir  250 . 
         [0027]    In one embodiment, the scale  270  may measure the amount of fluid (by mass) that may be added to the reactor  100 . The scale  270  may comprise a measuring instrument  290   a  that may be used to measure the weight of the fluid in the reservoir  260 . This measurement may also be used as feedback to the automated control system to control the pump  120 . Input may be provided to the pump  120  to precisely control the flow of the fluid by receiving a signal from the automated control system. For example, the automated control system may engage the pump  120  until the measurement instrument  290   a  indicates that a certain weight of fluid has been pumped into the reactor  100 . 
         [0028]    Precise volumes of fluid may also be delivered by controlling the pump  120 . For example, if pump  120  is a peristaltic pump, a certain number of revolutions (or partial revolutions) may be controlled by the automated control system to supply a certain amount of delivery fluid. This may be useful during the addition mode, especially if the density of the fluid is known and homogeneous and where the amount of fluid introduced to the reactor  100  is important. 
         [0029]    The temperature of the delivery fluid may also be monitored at a number of points in the system  205  as feedback to the automated control system. For example, temperature measuring instrument  290   b  may measure the temperature of the fluid in the reservoir  250 , the heat exchanger  280 , any of the delivery lines (e.g., lines  160 ,  220 , or  240 ), the valve system  210 , or any other point where the temperature of the fluid may be taken. 
         [0030]    In another embodiment, system  205  may comprise heat exchanger  280 . In certain embodiments, heat exchanger  280  may replace heater  260 . Heater exchanger  280  may employ a heat transfer liquid to heat the solution or slurry as it is transferred from reservoir  250 . Heat exchanger  280  may also be controlled, for example, by the automated control system using feedback from one or more of the temperature sensors  290   b . In this embodiment, a temperature measurement of the system  205  may be fed back to the automated control system to control the heat exchanger. In this embodiment, pump  120  may run continuously until fluid is needed to be added to the reactor  100 . 
         [0031]    As shown in flow diagram  300  ( FIG. 3 ) and diagram  400  ( FIG. 4 ), fluid flow in the systems  200 ,  205  (see  FIGS. 2A / 2 B and  2 C, respectively) may also controlled by the use of a timer such that, after a certain time interval, the flow of the delivery fluid is circulated (i.e., in circulation mode) to the heating system for a certain time interval to warm the delivery fluid and circulation may be halted for a second time interval. This circulation process may then be repeated. By selecting appropriate time intervals the system may be used to ensure that the fluid does not cool and solidify, to prevent blocking of the lines. 
         [0032]      FIG. 3  describes a control process flow of system  205  where a scale measurement  290   a  measures the weight of the fluid in the reservoir  250 . Initially, the system may be purged of oxygen and moisture ( 310 ) by placing the valves into circulation mode (valves  215 ,  218  both placed in position A). Inert gas may then be introduced and the pump run until the system is purged. The addition side of the system may also be purged in a similar manner by switching valve  218  to the B position. 
         [0033]    Once the system is purged, heater  260  may be activated and the fluid heated and stirred as described above ( 320 ) with the valve system  210  positioned in circulation mode ( 330 ). To maintain a temperature of the fluid and to prevent blockages of the delivery lines, the fluid in the supply and return lines may be circulated. For circulation of the fluid, the pump  120  may be turned on for a time interval T 1  and then turned off for a time interval T 2  ( 340 ). Time intervals T 1  and T 2  may be adjusted to ensure that the contents of lines  160 ,  220  and  240  remain mobile. For certain slurries, for example, T 1  may be five minutes and T 2  may be fifteen minutes. In other words, every twenty minutes, the slurry will circulate for five minutes. This circulation may be continued until an operator (or automated control system) determines that the fluid should be added to the reactor ( 355 ). 
         [0034]    After the decision to add fluid to the reservoir is made, the pump may be turned off for a time interval T 3  ( 370 ) to allow the system to stabilize before positioning the valves into addition mode (i.e., valve  215  in the A position and valve  218  in the B position). T 3  may be twenty seconds for example. The pump  120  may then be activated ( 290 ) and, in one embodiment, feedback from the scale  270  will indicate when an appropriate amount of delivery fluid (by mass) has been added as described above. Once the desired amount of delivery fluid is added, the pump  120  may be turned off for a time interval T 4  ( 395 ) to allow the system to stabilize and to allow for the valve system  210  to reconfigure into circulation mode. The valve system may then be configured with both valve  215  and valve  218  in the B position ( 397 ) to purge delivery line  240  of fluid before switching valve system  210  to the recirculation state—i.e., with both valve  215  and valve  218  in the A position. The process may then be repeated any desired number of times. 
         [0035]    In yet other embodiments, a mass flow meter such as a Coriolis mass flow meter, for example, may be used to measure the quantity of reactant slurry or solution delivered to the reactor. In certain embodiments, the mass flow meter may be placed in delivery line  240 . 
         [0036]    Another method for supplying the desired amount of fluid to reactor  100  is shown in flow diagram  400  of  FIG. 4 . Steps  310  through  380  are the same as those described above in connection with flow diagram  300 . However the process depicted in flow diagram  400  uses the flow rate of pump  120  to accurately control the addition of delivery fluid to the reservoir  100  during addition mode. Here, the pump may be run for a pre-determined amount of time T 5  ( 410 ) instead of weighing the delivery fluid. Once the desired amount of delivery fluid is added, the pump  120  may be turned off for a time interval T 6  ( 415 ) to allow the system to stabilize. The valve system may then be configured with both valve  215  and valve  218  in the B position ( 417 ) to purge delivery line  240  of fluid before switching valve system  210  to the recirculation state—i.e., with both valve  215  and valve  218  in the A position. As with the embodiment of flow diagram  300 , the process of flow diagram  400  may be repeated any desired number of times. For certain positive displacement pumps, the flow rate may be derived from the cycle time of the pump. Alternatively, for certain types of pumps, the total volume supplied by the pump may be derived from the number of cycles of the pump. 
         [0037]    While the reactor system disclosed herein may be particularly suitable for the synthesis of quantum dot materials, it will be appreciated that the system may also be suitable for any process in which it may be necessary to transfer a slurry from one vessel to another while maintaining temperature control. Moreover, it will be appreciated that many configurations for providing circulation of a slurry are possible and the scope of the invention is not limited to the specific configurations of valves, lines, and vessels described herein. 
         [0038]    Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as literally and equivalently covered by the following claims.