Abstract:
A thin-film evaporator comprising a vertical drum ( 1 ), a supply line ( 4 ) that is arranged in the upper region of the drum ( 1 ) and is used to supply a medium to be evaporated, a heating jacket ( 3 ) arranged on the periphery of the drum and forming vapours, a discharge line ( 20 ) for discharging the residue left in the lower end of the drum, and a condenser ( 11 ) supplied with a coolant, for increasing the separating capacity and optionally for performing chemical reactions, is characterized in that an inner device ( 24 ) influencing the action of the thin-film evaporator is provided in the path of the vapours from the heating jacket ( 3 ) to the condenser ( 11 ).

Description:
[0001]     This is a continuation of International Application No. PCT/AT2004/000335, filed on Oct. 1, 2004.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a thin-film evaporator comprising a vertical drum, a supply line that is arranged in the upper region of the drum and is used to supply a medium to be evaporated, a heating jacket arranged on the periphery of the drum and forming vapours, a discharge line for discharging the residue left in the lower end of the drum, and a condenser supplied with a coolant.  
         [0003]     Temperature-sensitive substances such as, for example, pharmaceutical solutions or food concentrates may be heated to the boiling point only temporarily. So-called thin-film evaporators in which the medium to be evaporated or the solution to be concentrated by evaporation, respectively, is applied to the evaporator area only as a thin film serve for meeting this demand. The result of this is just a short contact time with the heating surface so that thermally unstable liquids and substances, respectively, can also be used and are only exposed to a low evaporation temperature, in particular also under a vacuum or at a very low pressure. Furthermore, thin-film evaporators are used for separation tasks if the product accumulating as a residue has poor flow properties and/or is prone to agglutinations.  
         [0004]     Thin-film evaporation processes are based on the principle of simple distillation according to which the separating capacity of said type of evaporator is limited. Thin-film evaporators are available in various designs, for example as falling-film evaporators or as rotary evaporators (known from Chemie Technik by Dr. Ing. Eckhard Ignatowitz, 5 th  edition, Europafachbuchreihe, page 306).  
       SUMMARY OF THE INVENTION  
       [0005]     It is the object of the invention to improve the evaporator type thin-film evaporator in terms of increasing the separating capacity, whereby, advantageously, also a saving of energy—preferably both of cooling and heating energy—and optionally also a chemical reaction during the evaporation process are supposed to be feasible and/or accelerable, respectively.  
         [0006]     In case of an evaporator type thin-film evaporator, this object is achieved according to the invention in that an inner device influencing the action of the thin-film evaporator is provided in the path of the vapours from the heating jacket to the condenser, with the inner device advantageously being designed with a circular cross-section and preferably being arranged so as to be equally distant from the condenser or directly resting on the exterior of the same.  
         [0007]     Thereby, the inner device is suitably designed as a mass transfer area.  
         [0008]     According to a preferred embodiment, the inner device is designed as a catalyst, in particular as a heterogeneous catalyst.  
         [0009]     Efficient energy saving can be achieved in that the inner device is designed as a heat-exchange surface and preferably is connected to a supply line for the medium to be evaporated in order to preheat the medium to be evaporated.  
         [0010]     According to the invention, a rotary thin-film evaporator is characterized in that the inner device between the condenser and a wiping device movable on the inside along the drum jacket is provided for a medium to be evaporated which is introduced into the drum from above.  
         [0011]     The invention can also be used for a falling-film evaporator, with said evaporator exhibiting at least two drums.  
         [0012]     Depending on the design of the thin-film evaporator, the condenser is arranged in the central region of the drum or outside of the drum.  
         [0013]     If the condenser is arranged outside of the drum, it may exhibit an additional heat-exchange surface for preheating the medium to be evaporated.  
         [0014]     According to a preferred embodiment, a supply line for a substance, especially a liquid, influencing the action of the thin-film evaporator, such as a reaction liquid, a washing liquid or a residue or a distillate, is conducted to the inner device.  
         [0015]     The inner device can be configured as a wire double cylinder and preferably can be filled with filler materials or catalysts or can also be designed as a knitted wire fabric or as a cylindrical sealing ring.  
         [0016]     A preferred embodiment is characterized in that the inner device is movable in the space between the heating jacket and the condenser and, in particular, can be set in rotation, whereby, suitably, the inner device is movable with the mixing device and, in particular, is coupled to the same. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the following, the invention is illustrated in further detail by way of several exemplary embodiments with reference to the drawing wherein thin-film evaporators are shown in schematic sectional views, with  
         [0018]     FIGS.  1  to  7  and  12  in each case showing rotar evaporators.  
         [0019]     FIGS.  8  to  11  illustrate fittings of the rotary evaporator according to  FIG. 7 , and  
         [0020]     FIGS.  13  to  16  illustrate fittings of the rotary evaporator of  FIG. 12 .  
         [0021]     In  FIG. 17 , a falling-film evaporator is illustrated, and  
         [0022]      FIG. 18  shows a section taken along line AA transversely to the longitudinal axis of said evaporator.  
         [0023]      FIGS. 19 and 20  show further variants. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]     The rotary evaporator according to  FIG. 1  has an upright cylindrical drum  1  closed at the top and at the bottom, whose cylindrical part  2  is surrounded by a heating jacket  3 . In the upper region of the drum  1 , a supply line  4  for the medium to be evaporated is provided. A rotor  5  comprising a wiping device  6  is arranged in the drum  1 , which rotor is actuatable by a motor  7  arranged outside of the drum  1 . The supply line  8  for a heating medium is located at the lower end of the heating jacket  3 , the discharge line  9  for the heating medium is located at the upper end thereof.  
         [0025]     If water vapour is used as a heating medium, the supply line is located at the upper end of the heating jacket and the discharge line of the condenser is located at the lower end.  
         [0026]     The rotor  5  is arranged in a suspended manner via a pivot bearing only at the upper end of the drum  1  and is designed as a cylindrical basket open at the bottom.  
         [0027]     The medium to be evaporated is applied from above to the interior wall  10  of the cylindrical part  2  of the drum  1  and runs down the interior wall  10  as a liquid film, with the medium being heated to the boiling point. As the liquid film of the medium is running down, the liquid is repeatedly spread on the interior wall  10  of the drum  1  by the wiper blades of the wiping device  6  of the rotor  5 , whereby the evaporation process is accelerated.  
         [0028]     A condenser  11 , through which a cool medium flows, is located in the centre of the drum  1 . The supply line  12  for the coolant and the discharge line  13  for the coolant are located at the lower end of the drum  1 .  
         [0029]     According to the invention, the condenser  11  is surrounded by a further condenser  14  which thus ends up lying between the centrally arranged condenser  11  and the rotor  5  and the wiping device  6  thereof. The hot vapours formed from the medium to be evaporated are condensed at the two condensers  11  and  14  and flow along the same to the lower end of the drum  1 , where the drain  15  for the distillate is located.  
         [0030]     According to the invention, the medium to be evaporated is supplied via a supply line  16  to the condenser  14  arranged between the centrally arranged condenser  11  and the wiping device  6  and is preheated via the same as the hot vapours are being condensed. Said preheated medium to be evaporated then reaches the upper end of the drum  1  via a discharge line  17  of the condenser  14  and a duct  18 , where it is introduced via the supply line  4  and is distributed radially outwards onto the interior wall  10  of the drum  1 , using the rotor  5 .  
         [0031]     The residue, i.e. the portion of the medium to be evaporated which has not been evaporated, flows over the interior wall  10  of the drum  1  to the lower end, where it is collected in an annular chamber  19  and discharged from the drum  1  via a discharge line  20 . A vacuum pump is indicated by  21 .  
         [0032]     According to the embodiment illustrated in  FIG. 2 , the condensers  11 ,  14 , which in  FIG. 1  are arranged inside the drum  1 , are provided outside of the drum  1  in a separate cylindrical receptacle  22 . The hot vapours are withdrawn at the upper end of the drum  1  and are conducted to the condensers  11  and  14  via a pipe  23  connecting the drum  1  with the receptacle  22  in which the condensers  11  and  14  are located. In this case, the vacuum pump  21  is connected to the receptacle  22 . The annular chamber  19  for collecting the residue is unnecessary in this embodiment; the residue is withdrawn at the lower end of the drum  1 .  
         [0033]      FIG. 3  illustrates a rotary evaporator of a design similar to that shown in  FIG. 1 , wherein, however, no preheating of the medium to be evaporated is provided in the interior of the drum  1 ; rather, in this case, an inner device  24  is provided between the centrally arranged condenser  11  passed through by the coolant and the wiping device  6 , such as, for example, a wire double cylinder forming a cylindrical annular chamber roughly having the height of the cylindrical part  2  of the drum  1 . It is possible to provide catalysts or filler materials, respectively, in said cylindrical annular chamber for increasing the mass transfer area formed by the inner device  24 . Via a further supply line  16  at the upper end of the drum  1 , it is possible to supply a reaction liquid, a washing liquid or also a distillate to said inner device  24  between the condenser  11  and the wiping device  6 .  
         [0034]     The embodiment according to  FIG. 4  again differs from that according to  FIG. 3  in that the condenser  11  is arranged in a separate receptacle  22 , which, in analogy to  FIG. 2 , communicates with the drum  1  via a pipeline  23 .  
         [0035]      FIG. 5  illustrates the supply of distillate to the inner device  24  of a thin-film evaporator designed in analogy to the one shown in  FIG. 3 , which inner device is arranged between the condenser  11  and the wiping device  6 .  
         [0036]      FIG. 6 , in turn, shows the counterpart thereof comprising an external condenser  11 .  
         [0037]     In  FIG. 7 , a modified rotary evaporator is illustrated which exhibits a snakelike condenser  11 , over which a knitted wire fabric  27  closed on the top side is placed. The lower part of the knitted wire fabric  27  is formed by a cylindrical pipe  28  which is designed such that it rests on an outlet nozzle  29  for the distillate and the waste gas, respectively, thus causing a separation between the condenser space  30  and the evaporator space  31 . Due to a partial contact with the condenser  11 , the knitted wire fabric  27  has the effect that a part of the distillate gets into the knitted wire fabric  27  and thus is available for mass transfer.  
         [0038]     On the bottom side of the rotor  5 , a backup ring  32  is provided which has the function of collecting excess liquid dripping from the knitted wire fabric  27  which forms the inner device and conducting the same to the evaporator area, i.e. to the interior  10  of the drum  1 , via the centrifugal force caused by the motion of rotation. At the upper end of the drum  1 , the supply pipe  33  for charging the feed material is attached.  
         [0039]     According to the rotary evaporator illustrated in  FIG. 12 , a wire double cylinder  34  which serves for receiving a catalyst is provided above the condenser  11 . The lower part of the wire double cylinder  34  forms a ring  35  which rests on the outlet nozzle  29  for the distillate, thus providing a separation between the condenser space  30  and the evaporator space  31 . The upper part of the wire double cylinder  34  has an open design so that the liquid supplied via a feeding disk  36  reaches, via bores  37 , also the catalyst located in the wire double cylinder  34 . The bottom side of the rotor  5  also exhibits a backup ring  38  which serves for collecting excess liquid dripping down from the inner device  34  and conducting the same to the evaporator area, i.e. to the interior  10  of the drum  1 , via the centrifugal force caused by the motion of rotation. At the upper end of the drum  1 , a supply line  4  for the feed material and a supply line  33  for charging a liquid are provided.  
         [0040]      FIG. 17  shows a falling-film evaporator comprising several drums  1  which, in each case, are flushed by a heating medium and altogether are installed in a receptacle. A condenser  11  is fitted centrally for each drum  1 , and an inner device  24 ,  27  or  34  is installed between said condenser and the interior wall  10  of the drum  1  according to one of the above-described embodiments.  
         [0041]     According to a further variant, the inner device can also rotate. As a result, the liquid phase which has been supplied or has been deposited on the inner device or has condensed, respectively, is completely or partially returned to the evaporator area via the centrifugal force produced by rotation. Two variants with a rotating inner device  24  are illustrated in  FIGS. 19 and 20 . These embodiments are according to those illustrated in  FIGS. 5 and 6 . In each case, the inner device  24  is connected to the rotating wiping device  6 —and thus is actuated by the motor  7 .  
         [0042]     The following examples illustrate the use of the thin-film evaporators according to the invention.  
       EXAMPLE 1  
       [0043]     780 g of fatty acid methyl ester was distilled at a pressure of 0.2 mbar in a thin-film evaporator according to  FIG. 7 —however, without a knitted wire fabric  27 . The temperature of the heat transfer oil amounted to 165° C. The yield (distillate/amount used) of distillate amounted to 97.8%. A sample of the distillate was examined by scanning electron microscopy. Traces of salt crystals (size approx. 1 μm) were found.  
         [0044]     The same starting product was distilled in the same apparatus under the same conditions, however, a knitted wire fabric  27  closed on the top side was placed over the internal cooling coil.  
       Result  
       [0045]     A sample of the distillate was again examined with the scanning electron microscope. Neither traces of crystalline substances nor other impurities were found. A special advantage of the knitted wire fabric is that splashes of the medium to be evaporated do not reach the condenser  11  and thus do not get into the residue.  
       EXAMPLE 2  
       [0046]     A thin-film evaporator according to  FIG. 1 —however, without a condenser  14 —having an evaporator area of 9 m 2  was continuously charged with a feed flow of 1,820 kg/h. The feed temperature amounted to 40° C. The evaporator was heated with high-pressure steam at 20 bar abs, with the heating temperature being adjusted via pressure valves. The distillation pressure amounted to 0.8 mbar. 1,690 kg/h was withdrawn as a distillate. The residue amounted to 112 kg/h. This is equivalent to a residue ratio (residue/distillate) of 6.6%. 598 kg/h of water vapour was consumed in this adjustment.  
         [0047]     In a further step, the feed flow was conducted under constant conditions through a pipe coil which functioned as a preheater and as a condenser  14  and was wound around the central condenser  11 .  
       Result  
       [0048]     The feed temperature before entering the evaporator could be raised to 129° C. The steam consumption of the distillation decreased to 406 kg/h.  
         [0049]     This is equivalent to an energy saving of 32%.  
       EXAMPLE 3  
       [0050]     In two experiments, 800 g of a glycerol phase were distilled in each case at a pressure of 1.3 mbar in a thin-film evaporator according to  FIG. 7 —however, without a knitted wire fabric for the first experiment. The composition of the glycerol phase and of the distillate recovered in Experiment 1 (amount 656 g) can be seen in Table 1.  
         [0051]     For Experiment 2, the following modifications were performed on the evaporator. A knitted wire fabric  27  (mesh width 1 mm; wire diameter approx. 0.2 mm; wound in several layers; total thickness approx. 4 mm) closed on the top side was placed over the internal condenser  11 . The lower part was formed by a cylindrical pipe  28  which was designed such that it could be placed over the outlet nozzle  29  for the distillate and the waste gas, respectively, thus providing a separation between the condenser space  30  and the evaporator space  31 . The partial contact of the knitted wire fabric  27  with the condenser  11  thus created the precondition for a part of the distillate to get into the knitted wire fabric  27  in order to be available for the mass transfer.  
         [0052]     In the lower third of the rotor  5 , an additional backup ring  32  was fitted which had the function of collecting the liquid dripping down from the knitted wire fabric  27  and conducting the same to the evaporator area  10  via the centrifugal force caused by the motion of rotation.  
       Result  
       [0053]     The operating parameters for Experiment 2 were the same as for Experiment 1. 658 g of distillate was obtained. The composition of the distillate (see Table 1) produced higher purities in terms of the high-volatile and low-volatile components.  
                                             TABLE 1                       Example 3                   Conc. in   Charge   Distillate   Distillate       % by weight   Experiments 1 + 2   Experiment 1   Experiment 2                                Glycerol   84.7   97.6   98.9       Water   0.4   0.3   0.1       Ashes   5.8   0.1   n.n.       MONG   9.1   2.1   1.0       (calculated)       Ester   2.6   0.2   0.08                  
 
       EXAMPLE 4  
       [0054]     In Experiments 3, 4 and 5, 800 g of a fatty acid methyl ester phase were distilled in each case at a pressure of 0.5 mbar in a thin-film evaporator according to  FIG. 12 —however, without an inner device  24  for Experiment 3.  
         [0055]     For Experiments 4 and 5, the following modifications were performed on the evaporator. A wire double cylinder  34  (mesh width 1 mm; wire diameter approx. 0.2 mm; total thickness (outer radius—inner radius) approx. 10 mm) filled with the catalyst amberlyst (=amine-substituted solid ion echanger)  15  was placed over the internal condenser  11 .  
         [0056]     The lower part was formed by a ring  35  which was designed such that it could be placed over the outlet nozzle  29  for the distillate and the waste gas, respectively, thus providing a separation between the condenser space  30  and the evaporator space  31 .  
         [0057]     The upper part had an open design so that the liquid supplied via the feeding disk  34  could reach, via bores  37 , the catalyst located in the wire double cylinder  24 .  
         [0058]     The ring  35  on the bottom side of the rotor  5  had the function of collecting the excess liquid dripping down from the inner device  34  and conducting the same to the evaporator area  10  via the centrifugal force caused by the motion of rotation.  
         [0059]     Via an additional nozzle  33  in the upper part of the evaporator, 100 g of oleic acid was steadily added throughout the Experiment 5, which oleic acid could reach the inner device  34  via the feeding and distributing disk  36 , respectively, in order to react with the methanol contained in the fatty acid methyl ester phase.  
         [0060]     The operating parameters for Experiments 4 and 5 were the same as for Experiment 3 which was carried out without the inner device  34  and without the addition of oleic acid, respectively.  
       Result  
       [0061]     The amounts and compositions of the feed materials and distillates in the experiments are indicated in Table 2.  
         [0062]     In Experiment 4, the neutralization number was lower than in Experiment 3, since free fatty acid and methanol reacted in the evaporator to form fatty acid methyl ester.  
         [0063]     In Experiment 5, the amount of fatty acid methyl ester was substantially higher and the neutralization number was lower than in Experiment 3, since free fatty acids of the starting product and oleic acid reacted with methanol in the evaporator to form methyl ester.  
                                                             TABLE 2                               Charge                           Experiments   Distillate   Distillate   Distillate       Example 4       3 + 4   Experiment 3   Experiment 4   Experiment 5                                Amount   g   800   760   760   810       Methyl ester   % by weight   94.7   97.6   97.8   98.9       Water   ppm   800   40   50   50       Methanol   % by weight   1.0   n.n.   n.n.   n.n.       Neutralization   mg KOH/g   0.4   0.35   0.07   0.09       number                  
 
       EXAMPLE 5  
       [0064]     In Experiments 6 and 7, 800 g of a methyl ester phase were distilled in each case at a pressure of 0.5 mbar in a thin-film evaporator according to  FIG. 12 —however, without an inner device  34  for Experiment 6.  
         [0065]     For Experiment 7, the following modifications were performed on the evaporator. A wire double cylinder  34  (mesh width 1 mm; wire diameter approx. 0.2 mm; total thickness (outer radius—inner radius) approx. 10 mm) filled with glass beads (diameter 4 mm) was placed over the internal condenser  11 .  
         [0066]     The lower part was formed by a ring  35  which was designed such that it could be placed over the outlet nozzle  29  for the distillate and the waste gas, respectively, thus providing a separation between the condenser space  30  and the evaporator space  31 .  
         [0067]     The upper part has an open design so that the liquid supplied via the feeding disk  36  could reach, via bores  37 , the glass beads located in the wire double cylinder  34 .  
         [0068]     The backup ring  38  on the bottom side of the rotor  5  had the function of collecting the excess liquid dripping down from the wire twin basket  24  and conducting the same to the evaporator area  10  via the centrifugal force caused by the motion of rotation.  
         [0069]     Via an additional nozzle  33  in the upper part of the evaporator, 80 g of trioctylamine was steadily added throughout the Experiment, which trioctylamine could reach the inner device  34  via the feeding disk  36  in order to absorb substances from the gas phase.  
         [0070]     The operating parameters for Experiment 7 were the same as for Experiment 6 which was carried out without said fitting.  
       Result  
       [0071]     As a result of the modification, a higher purity of the distillate was achieved in Experiment 7 (see Table 3).  
                                                 TABLE 3                           Charge   Distillate               Exper-   Exper-   Distillate       Example 5   iments 6 + 7   iment 6   Experiment 7                                Amount   g   800   760   756       Methyl ester   % by weight   94.7   97.6   97.9       Water   ppm   800   40   35       Methanol   % by weight   1.0   n.n.   n.n.       Neutralization   mg KOH/g   0.4   0.35   0.05       number                  
 
       Summary  
       [0072]     The particular advantages of the thin-film evaporators according to the invention consist in an increase of the separating capacity by installing mass transfer areas directly in the evaporation space, in the charging of a reflux to the mass transfer area, in the recirculation of the liquid flow to the evaporator area as well as in the charging of a washing liquid.  
         [0073]     By means of the thin-film evaporators according to the invention, chemical reactions can be carried out, namely by installing heterogeneous catalysts in the evaporation space and/or by installing mass transfer areas as well as by adding reactants directly into the evaporation space. According to the invention, combinations of distillation, absorption and chemical reaction can thus be realized.  
         [0074]     Pipes, packings, knitted fabrics, filler materials or floors might be considered as suitable mass transfer areas.  
         [0075]     Furthermore, substantial energy savings during the operation of the thin-film evaporator are rendered possible by the installation of temperature-exchange surfaces as illustrated, e.g., in  FIG. 1 .