Abstract:
A process and an apparatus separate a volatile component from a substance mixture (raw product). The substance mixture is heated, the volatile component is at least partly evaporated and then the vapor formed is condensed. To improve the separating action, the condensate, in the region of the point of condensation, is contacted with a liquid in which the condensate dissolves.

Description:
BACKGROUND 
     The invention relates to a process for separating one or several volatile component(s) from a substance mixture, in which the substance mixture is heated, the volatile component(s) is/are at least partially evaporated and the then formed vapor is condensed. In addition, the invention relates to a device suitable for performing said process. 
     The pre-requisites for distillation processes of the mentioned type are that the component(s) to be separated has/have a lower boiling point than the other component(s) of the substance mixture and that with respect to the component(s) to be separated, a vapor pressure gradient is maintained between the location of the evaporation and the location of the condensation. 
     The term “flash distillation” generally means a vacuum distillation technique in which evaporator and condenser are arranged in one and the same vessel in such manner that the vapor molecules travel a short path from the location of the evaporation to the location of the condensation. Normally, the distance between evaporator and condenser surface in industrial flash distillation apparatuses amounts from a few centimeters up to several decimeters. If the distance between evaporator surface and condenser surface is smaller than the average free path length of the vapor molecules, one talks of molecular distillation. 
     Based on low operating pressures, flash distillation and molecular distillation are, among others, excellent methods for distillative separation of one or several volatile components from bi- or multi-substance mixtures with low operating temperatures. The method, however, always reaches its limitation if the vapor pressure of the distilled component or components on the condensation surface reaches the partial pressure of the corresponding component(s) in the mixture on the heated evaporator wall. Further separation of the volatile component(s) is then no longer possible, since, according to the understanding of flash distillation, the driving force, i.e. the pressure difference, is lacking, or according to the understanding of molecular distillation, the evaporation rate at the evaporator surface corresponds to the evaporation rate of the respective component(s) on the interior condenser. Further lowering of the interior condenser temperature in order to reduce the vapor pressure of the volatile component(s) over the condensate flow on the interior condenser is frequently not possible, because the condensate would solidify, for example. 
     SUMMARY 
     It is the object of the present invention to improve a distillation method. 
     The condensate, according to the meaning of the invention, is brought into contact with a liquid, in which it dissolves. Thus, concentration and vapor pressure of the component to be condensed, are lowered in the area of the place of condensation. The vapor pressure gradient between the place of evaporation and the place of condensation is hereby increased, thereby achieving an improvement in the degree of separation. 
     It is of particular benefit to perform the invention-specific method under conditions of flash- or molecular distillation and/or to employ for the execution of the invention-specific method a flash distillation- or molecular distillation apparatus, which is equipped with means for supply and outward transfer of that particular liquid which serves to dissolve the condensate. Inasmuch as said liquid has the effect of lowering the concentration of the volatile component by diluting the condensate, it is hereinafter also called washing fluid. 
     It does not matter with respect to the invention-specific process whether the evaporation takes place from a mechanically wiped film or from an un-wiped film flowing steady or turbulent on the heated evaporator surface. It likewise does not matter whether the evaporation takes place as with the classical flash evaporator, from a heated evaporator surface surrounding the condenser, onto a washing fluid trickling film, or vice-versa, from an evaporator surface arranged inside the apparatus to a trickling film flowing down the interior wall of the apparatus. In principle, all configurations of evaporator surfaces and condenser surfaces are possible, in which, for example, the boundary conditions of flash distillation or molecular distillation are maintained. 
     The washing fluid must, on the one hand, have the property of dissolving the volatile component to be separated. Additionally, the washing fluid must have a sufficiently low vapor pressure. In the event that the washing fluid is a substance mixture and/or a volatile substance mixture that is to be separated, all components of the respective substance mixtures must have the mentioned properties. 
     In a beneficial embodiment of the invention-specific process, a trickling film is generated with the aid of the washing fluid, which flows and is maintained on the surface of a cooled condenser. An externally cooled condenser can be done away with if the washing fluid itself is adequately cooled in such fashion that its surface forms the condensation surface. In case of the latter, it is possible to even do without a surface on which the washing fluid flows down. It suffices, for example, if the washing fluid flows in form of droplets in the vicinity of the evaporator surfaces. 
     If an installation is used, on which the washing fluid trickles down, then it is appropriate to provide its surface with unevenness, which causes swirling of the washing fluid. It is also possible to preferably employ a wire mesh as installation. 
     The substance or the substance mixture applied for producing the trickling film can be transferred outward from the apparatus by means of a single pass-through or also by means of circulating the volatile component(s) until attaining the desired enrichment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional benefits and details of the invention are going to be explained using exemplary embodiments, represented schematically in  FIGS. 1 to 9 . 
         FIGS. 1 to 3  depict a distillation apparatus according to the invention, 
         FIGS. 4 and 5  depict an exemplary embodiment according to the invention, in which tempering of condensation surface takes place by means of a heating-/cooling medium, which is independent of the employed washing fluid, 
         FIGS. 6 ,  7  depict an exemplary embodiment in which the tempering of the condensation surface is done by the washing fluid itself, 
         FIG. 8  depicts an exemplary embodiment in which the cooled washing fluid is carried along a wire mesh, and 
         FIG. 9  depicts the results of distillation processes relative to the separation of caprylic acid from sun flower oil. 
     
    
    
     DETAILED DESCRIPTION 
     In the apparatus  1  according to  FIG. 1 , the vessel is identified with  2 , the thermal casing with  3 , the evaporator surface with  4  and the condenser with  5 . The condenser  5  is shown in dotted lines. This is to indicate that in the event that the washing fluid is self-cooled, the condenser need not be present. We will deal more specifically with this variation below. The evaporator chamber is identified with  6 , and, as customary, designed essentially cylindrically. 
     Addition of the raw product takes place via line  7 , on a plate  8 , arranged in the upper region of vessel  2 , mostly operating in rotating fashion, whose task it is to conduct the raw product to the walls of vessel  2  and/or the evaporator surface  4  in such manner that is flows down on the evaporator surface as trickling film  9 . The liquid film  9  leaving the evaporator surface  4  collects in the outer channel  10  and is transported out via line  11 . Supply and removal of thermal medium to/from thermal casing  3  takes place via lines  12  and  13 . 
     The condenser  5 , designed as pipe coil, is cooled internally. Charge and discharge of cooling agent/thermal carrier takes place via lines  14  or  15 . 
     Above condenser  5  is located another plate  16 , which is equipped with a weir  17  (see also  FIGS. 2 and 3 ). Weir  17  is located above the pipe coil  5  and is equipped with pass-through apertures  18  as well as a downwardly oriented edge  19  facing the upper pipe coil. 
     Supply of washing fluid to condenser  5  takes place via plate  16 . In the center of plate  16  there is an opening  20  into which issues an ascending pipe  22 . This is supplied with washing fluid from below via connection line  23 . The interior wall of the annular chamber  10  forms a centrally located chamber  24  in which collects the washing fluid which flows from condenser  5  in downward direction and is transferred out via line  25 . An evacuation device connected to vessel  2  is represented only schematically and identified with  26 . 
     During operation, the low-boilers evaporate from the evaporator surface  4 . The vapor flows in direction of the condenser  5 . The washing fluid reaches plate  16  via ascending line  22  and flows through the apertures  18  to the outside and downward. Washing fluid flowing along the drip edge  19  wets the surface of the condenser  5 . There, the washing fluid dissolves the condensates of the low-boiling substance, which get into chamber  24 , together with the washing fluid and are discharged via line  25 . The dissolution and discharge of the condensate of the low-boiling substances with the washing fluid has the result—as indicated above—of lowering the vapor pressure of the low-boiler in the region of the condensation surface and thus the desired increase of vapor pressure gradient from the evaporator surface  4  to the condenser  5 . 
     With one (or several) valve(s) it is possible to effect an exchange of washing fluid in continuous or intermittent fashion. If desired, the washing fluid can be prepared in a subsequent process and used again. It is also conceivable to segregate from the supply of the substance to be processed, a portion, either continuously or intermittently, and to employ same as washing fluid. 
     According to the meaning of the invention, other embodiments of distribution plate  16  and weir  17  are also conceivable, for example with curved areas or structured surfaces, metal transport units for fluid control, fluid discharges etc. Likewise, the washing fluid can be applied to the condenser area by a differently designed fluid supply- or injection system. 
       FIGS. 4 and 5  indicate schematically another embodiment of a distillation apparatus according to the invention, in which the condenser  5  cools the washing fluid. The raw product is introduced above the thermal casing  3  and flows as film  9  down-ward on the evaporator surface  4 . The raw product film can flow freely as drop film or be wiped mechanically. Low-boiling components evaporate and flow on the surface of condenser  5 . Non-evaporated residue remaining in film  9  gets into the collection chamber  10  and leaves the vessel via line  11 . 
     The condenser is schematically represented as a unit with an integrated heat exchange device  28 . The supply of this device with cooling fluid takes place from below (lines  14 ,  15 ). 
     The washing fluid exits from aperture  20  on the upper side of the condenser  5 . It is already cooled while flowing through the ascending line  22 . Condensation and dissolution of the low-boilers evaporated on the evaporator surface  4  takes place in the free flowing or also wiped washing fluid film, which flows down on the surface of the condenser  5 . The washing fluid gets into the collection chamber  24  and leaves the vessel via line  25 . 
     In the exemplary embodiment represented in  FIG. 4 , the washing fluid is circulated. A conveyor pump  32  is located in line segment  31 , which connects the exit line  25  with the inlet line  22 . Exchange of washing fluid, either in continuous or intermittent fashion can take place via branch lines  33  and  34  having one valve each,  35 ,  36 . In the above described exemplary embodiments, the condenser  5  takes on the required cooling of the washing fluid. If the washing fluid itself is supplied at a sufficiently low temperature, supply of the condenser  5  with cooling fluid can be eliminated. Its surface, together with the washing fluid serves as condensation area. Finally, both, the condenser  5  and the washing fluid can also be cooled. 
       FIGS. 6 to 8  depict exemplary embodiments according to the invention where the washing fluid serves at the same time as cooling medium for the condensation process and as solvent for the condensing low-boilers. 
     The exemplary embodiment according to  FIGS. 6 and 7  corresponds to  FIGS. 4 and 5 . The condenser unit  5  in this embodiment is not cooled. In the line segment  31 , which connects the exit line  25  of the washing fluid with the inlet line  22 , a heat exchanger is located in addition to pump  32 . Pump  32  and heat exchanger  37  are appropriately regulated so that the washing fluid continuously enters the evaporator chamber  6  at  20  via line  22  at a sufficiently low temperature. Condensation of the low-boilers takes place in the film of the washing fluid which flows down on the surface of the condenser unit  5 . 
     In a particularly beneficial embodiment, a solid condenser unit  5  can be totally eliminated. The self-cooled washing fluid can be supplied, for example, in the described manner and trickle down freely from a plate  16 , as it is described relative to  FIG. 1 . Spraying of the washing fluid into the evaporator chamber is also possible. 
     The example according to  FIG. 8 , which corresponds to the embodiment according to  FIG. 1 , depicts a variation without condenser. Plate  16  connects in downward direction, at the height of the evaporator surface  4 , with a built-in unit  38 , which turbulently carries the washing fluid trickle-down film and which consists, for example, of an essentially cylindrically designed wire mesh arrangement. The built-in unit  38  extends as far as the lower collection chamber  24 . 
     The invention is not limited to the disclosed apparatus examples. The described process can be performed in almost all appropriately designed distillation fixtures. These may be made of metal, glass and/or other materials. 
     General Process Examples are: 
     Distilling of fatty acids from vegetable or animal oils; terpenes, steroids and alkaloids from vegetable and animal natural products; pesticides, herbicides or fungicides, as well as their decomposition products from vegetable and animal oils and fat; included are processes as disclosed in the International Applications WO 2004/007 654 A1 and WO 2004/007 655 A1. Separation of color- and aroma substances, vitamins, (co)-enzymes, tetra-pyrroles, polyphenols or fatty acid esters from vegetable and animal natural products; separation of monomers from di-, tri- and polymers; of monoesters from di-, tri- and polyesters; generally monomeric or dimeric coupling components from polymers or pre-polymers, which can be produced by addition or condensation. 
     As further example, a description is provided for separation by distillation of caprylic acid from a triglyceride mixture (sun flower oil). Starter product is a 0.5% solution of caprylic acid in sun flower oil. The named mixture is exemplary for a frequently encountered separation task in an industrial application of flash distillation, namely: as much reduction as possible of the remaining concentration of low-boilers from a high-boiling substrate. During such process, it is frequently not possible, for different reasons, to select the temperature of the interior condenser optionally low, which leads to the initially described reduced depletion performance of the evaporator. Utilization of the invention-specific washing condenser results, under these conditions, to a significant improvement in the stripping performance, i.e. lowering of attainable remaining contents of low-boilers in the distillation residue. For determining the experimental data, a washing condenser was employed of the design according to  FIG. 1 , which can be used as both, conventional interior condenser (no washing fluid feed) as well as washing condenser with controllable washing fluid flow. Sun flower oil was employed as washing fluid. It has been shown in distillation experiments with varying condenser temperatures and other constantly kept parameters, that in the examined temperature range, the invention-specific sprinkling of the condenser with washing fluid produces a lowering of the residue contents by up to 60% in comparison with ordinary condensation. The volume flow as well as the loading of the circulated washing fluid with condensed low-boilers can vary over a larger range without having a negative impact on the depletion.  FIG. 9  shows exemplary results of test distillations. The Figure indicates the residue contents (y-axis) at different condensation temperatures (x-axis). 
     The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.