Abstract:
A vacuum pressure controller for vacuum distillation equipment is controlled to mix a dilution gas with the distillation vapors to control the vacuum pressure to which the distillation equipment is subjected.

Description:
[0001]     This application claims priority of U.S. provisional application 60/662,157 filed Mar. 16, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a vacuum pressure controller of the type that is used for rotary evaporators, vacuum ovens and stationary distillation equipment  
       BACKGROUND OF THE INVENTION  
       [0003]     Vacuum pressure controllers are used in several chemical laboratory applications such as rotary evaporators, vacuum ovens and stationary distillation equipment. Of these, rotary evaporators are by far the predominant usage.  
         [0004]     Vacuum pressure controllers maintain present vacuum pressure during these distillation processes at temperatures typically not exceeding 180° C. and for volumes up to about 30 liters of distilled liquid. The typical process setup consists of a distillation apparatus, a condenser with a liquid collector, a pressure controller and a vacuum pump. A rotary evaporator is disclosed, for example, in U.S. Pat. No. 6,709,025. Chemicals used during distillation require maintaining pressure in the range of several Torr to a few hundred Torr.  
         [0005]     In these processes, the vacuum pump applies the vacuum to the system through a vacuum pressure controller. Prior controllers had different means of controlling the pressure. A pressure transducer was supplied to give a measurement of the pressure in the system and a controller controlled a valve to maintain the pressure set by the user. The valve, most typically an inline proportional or on-off valve, controlled the amount of vacuum applied to the distillation apparatus. Other systems would turn the vacuum pump on or off to control the amount of vacuum. These various methods sometimes shortened the pump life, required maintenance, or required time for the vacuum pump to recover from a low vacuum to a high vacuum.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention provides a vacuum pressure controller in which a dry gas, for example air, is bled into the vacuum stream in connection with maintaining the required vacuum pressure in the system. The gas bled into the vacuum stream dilutes the vapor, cools the mixture of vapor and gas admitted to the pump, prevents condensation in the vacuum pump. The result is a longer pump-life, longer maintenance intervals, a lower operation cost, and quicker recovery of the pump.  
         [0007]     Using the invention, the diluted vapor is less chemically aggressive on the pump and other parts of the system. In addition, the lower operating temperature of the vapor diluted with the gas lowers the pump temperature, which increases its life. The vapor diluted with air also helps prevent internal condensation in the pump and by always permitting a flow through the pump, it lowers oil contamination in oil-sealed pumps. Since the pump can be run at or near its full speed all the time, the pump will recover quickly to its original vacuum pressure once the bleed valve is shut.  
         [0008]     These and other features and advantages of the invention will be apparent from the detailed description and drawings.  
         [0009]     The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic view of a rotary evaporator system, including a vacuum pressure controller of the invention  
         [0011]      FIG. 2  is an enlarged cross-sectional view of the valve illustrated in  FIG. 1 ;  
         [0012]      FIG. 3  is a perspective view of the valve;  
         [0013]      FIG. 4  is a sectional view of an alternative embodiment of the rotary evaporator system wherein the vacuum pressure controller and pump are within the same housing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Referring to  FIG. 1 , the system  10  includes a rotary separator distillation apparatus  12 , a vacuum pump  14  and a vacuum pressure controller  16  of the invention. The vacuum pressure controller  16  includes an air bleed valve  18  and a control unit  20 . A first vacuum pressure line  22  connects the pump  14  to a manifold  24  of the unit  16  and a second vacuum pressure line  26  connects the manifold  24  to the rotary evaporator  12 . A pressure transducer  28  is in communication with the manifold  24  to provide an electrical signal indicative of the vacuum pressure within manifold  24 , which signal is input to control unit  20  by line  30 . Control unit  20  includes dial  32  and pressure gauge  34  for a user to dial-in the level of vacuum that the user desires the system to produce. Line  36  connects the output of control unit  20  to the control input of valve  18  and control unit  20  controls valve  18 , which may be a proportional valve or an on-off valve. Control unit  20  is similar to control units which have been used in prior vacuum pressure controllers that had in-line valves.  
         [0015]     The valve  18  has an intake port  40  into which outside air flows when the valve  18  is opened by the control unit  20 . Air entering the valve  18  through the port  40  flows through the valve  18  into the manifold  24  and there mixes with vapor entering inlet port  29  of the manifold  24  through the line  26 . The mixture of air and vapor then flows through the manifold  24  and out the outlet port  31  of the manifold  24  through the conduit  22 , into the pump  14 , and after flowing through the pump  14  may be discharged by the pump  14  through the outlet of the pump  14 .  
         [0016]      FIG. 4  includes all of the components of  FIG. 1 . The difference between the two embodiments is that the components of the pump and the vacuum pressure controller are configured so as to be disposed within the same housing as the pump. Schematically, however, both rotary vacuum pressure systems operate in the same manner. For clarity those components which are depicted in  FIG. 4  which correspond to a like component in  FIG. 1  are given the same number as  FIG. 1  except the reference numbers in  FIG. 4  all have the suffix “a”. Thus, for example,  20   a  refers to the controller of  FIG. 4  and  20  refers to the controller in  FIG. 1 .  
         [0017]     A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described but should be defined by the claims which follow.