EP2452071B1 - Method for delivering fluids - Google Patents

Description

The invention relates to a process for the continuous production of a liquid which is used as feedstock in a chemical process. The invention further relates to a process for the hydrogenation of aromatic compounds, in particular aromatic amines, and a process for the preparation of esters, wherein the starting materials are fed to the reactor by means of the inventive method for the continuous conveying of liquids. Another object of the present invention is the use of a product resulting from hydrogenation of an aromatic compound as an auxiliary liquid for conveying an aromatic compound and the use of an alcohol or an ester of alcohol and carboxylic acid as an auxiliary liquid for conveying carboxylic acids or carboxylic acid derivatives.

For the continuous promotion of hot and especially molten substances in a printing system in the literature, such as in Ullmann's Encyclopedia of Industrial Chemistry, High-Pressure Technology (Electronic Release DOI: 10.1002 / 14356007.b04_587), called various possibilities.
When using centrifugal pumps and centrifugal pumps either numerous pump stages must be connected in series to achieve the required high differential pressure, or a very high speed must be used. In order to prevent solidification of the product in the pump, very complex and thus cost-intensive designs for complete heating of all product-contacting components must be used. Therefore, this type of pump is usually used only for applications in which, above all, large volume flows are to be promoted.
To promote smaller volume flows, for example, heatable gear pumps can be used. A disadvantage of this type of pump, however, is that to drive the gears an outwardly guided and sealed drive shaft must be used and it can thus come to contamination of the fluid with sealants and lubricants or leakage of the fluid to the outside.
With a high-pressure diaphragm pump, this disadvantage is remedied, since the drive is effected by means of a hermetically sealed membrane and thus there can be neither contamination with sealants and lubricants nor leakage of the pumped medium to the outside. However, due to the low temperature stability of the membrane materials (eg polyethylene (PE) or polytetrafluoroethylene (PTFE)) and the incomplete heating, diaphragm pumps can not be used to convey hot liquids or melts. For this purpose, then either metallic membranes with completely heatable pump heads or so-called "pendulum pumping systems" must be used.

Pendulum pumping systems are used, for example, in the DE-A-1453576 . DE-A-1528547 . EP-A1-048535 . DE-A1-3021851 . DE-T5-19782185 . DE-A-2553794 . WO-A-80/01706 . DE-A-4124 290 or EP-B1-36945 disclosed.

DE-A-1453576 describes a device for pumping a corrosive liquid, such as ammonium carbamate solution, by means of a pendulum pump unit, which is divided into two elements. The first element ("main pump") causes a non-corrosive auxiliary liquid, such as water, in a lifting movement and thus drives the second pump element with two non-return flaps for conveying the corrosive liquid via a connecting line ("transfer line"). The auxiliary liquid is constantly fed via a small auxiliary pump to the connecting line.

DE-A-1528547 describes a nearly identical pump concept with continuous metering of neutral auxiliary fluid to the suspension line.

EP-A1-048535 describes a pendulum pump system for conveying a hot coal slurry, wherein an oil mixable with the coal slurry is used as the auxiliary liquid.

In DE-A1-3021851 a pendulum pump system is described, wherein the auxiliary liquid is preferably not miscible with the liquid to be delivered and in which the pendulum line is arranged spatially very compact.

In DE-T5-19782185 is a pendulum pump system for pumping hot media as well as solid / liquid mixtures ("slurries") with a similar pump as in DE-A-1453576 described, wherein the pendulum line is cooled in the horizontal part to prevent overheating of the main pump. On the addition of an auxiliary liquid is omitted here.

WO-A-80/01706 also describes a pendulum pump system for pumping hot liquids, wherein the connecting line consists of a horizontal and a vertical part and is also cooled.
A similar system will be in DE-A-4124 290 described.

DE-A-2553794 discloses a pendulum pump system with vertically mounted shuttle, wherein a temperature gradient between the hot liquid and the main pump is maintained by cooling.

EP-B1-36945 describes a similar pumping device, in which case a movable piston between the conveying fluid and auxiliary fluid to prevent their mixing.

When pumping hot liquids, the pump systems described in the prior art have disadvantages.

In high-pressure diaphragm pumps, the maximum permissible temperature of the pumped medium is generally limited by the resistance of the membrane material, for example when using plastic membranes, such as PE or PTFE membranes.
The use of metal membranes would lead to very large and therefore expensive pump heads due to their very low flexibility.
Furthermore, the pump heads of diaphragm pumps, especially on the membrane drive and on the membrane itself, are not completely heatable, so that it can lead to solidification (crystallization) during the pumping of melts and thus to the mechanical destruction of the membrane.

When using high-pressure piston pumps, a lubricating oil or similar fluid is usually required to lubricate the piston. This can mix with the liquid to be pumped and contaminate it. The heating of piston pumps is generally not completely possible, so that deposits can also form here at unheated areas of the pump.

High-pressure diaphragm pumps with a transfer line to a spatially separate pump body with suction and delivery valve are in principle suitable for conveying hot melts. However, the use of an auxiliary liquid for transmitting the pumping movement from the diaphragm pump to the melt to be conveyed is necessary for such a pump arrangement. A part of the auxiliary liquid can mix with the melt to be conveyed. This leads to contamination of the liquid to be delivered with the auxiliary liquid.

A cooling of the pendulum line usually leads after a short time to parts of the melt diffuse through the pendulum line in the direction of the main pump, there solidify and lead to blocking of the pump. Likewise, the use of auxiliary piston in the pendulum line would lead to rapid blockage of the piston by solidifying melt.

In US 4961688 , which is considered as the closest prior art, also a method for the continuous production of liquids by means of displacement pump and spatially separated delivery valves and a liquid-filled transfer line is described, in which case the shuttle also contains an auxiliary liquid whose melting point is below the melting point of the liquid to be conveyed. US 4961688 does not disclose, however, that the liquid to be delivered is used as feed in a chemical reaction and the auxiliary liquid is a product or reactant of the chemical reaction. This reveal also the documents FR 608718 and FR 877570 whose auxiliary liquid is a gas and not a liquid, not.

It was therefore an object of the invention to promote a liquid at high temperature without contamination by, for example, solvent or sealant in a high-pressure chemical reactor. In particular, the object was to reduce the formation of deposits and residues in the pump system in the transport of liquids that tend to form deposits. Liquids that can form deposits and residues are, for example, liquids that solidify themselves or their ingredients when falling below a minimum temperature, crystallize or fail. In particular, the object of the present invention was to develop a process for the promotion of organic melts and concentrated solutions of organic compounds, especially organic melts, which should be dispensed with costly designs for complete heating of all product wetted components, in particular the membrane of a diaphragm pump to keep investment and operating costs as low as possible.

The object underlying the invention has been achieved by a method for continuously conveying a liquid which is used as a starting material in a chemical reaction by means of positive displacement pump with spatially separated delivery valves and a liquid-filled transfer line between the positive displacement pump and delivery valves, characterized in that in the pendulum line a Auxiliary liquid is, which is a product or a reactant of the chemical reaction and has a melting point, which is below the melting point or below the saturation temperature of the liquid to be conveyed dissolved.

To carry out the method according to the invention, a pump system is used, which valves a positive displacement pump ("main pump") with spatially separated delivery and comprises a transfer line between positive displacement pump and delivery valves.
The delivery valves are generally housed in a housing. The housing together with the delivery valves therein is referred to hereinafter as "valve body".
The valve body generally has an inlet on the suction side and an outlet on the pressure side in each case. The inlet or the outlet are usually connected to a feed line on the suction side or a discharge on the pressure side, through which the liquid to be conveyed is conveyed.
The delivery valves are usually mounted at the inlet and outlet in the valve body so that the fluid to be delivered is passed through the valves.
The valves are generally designed so that the fluid to be pumped can pass the valves only from the suction side in the direction of the pressure side. The flow in the opposite direction (from the pressure side to the suction side) is generally blocked. For example, the valves can be designed as check valves, preferably ball check valves.
Between the valves is usually located in Ventilköper a cavity through which the liquid to be conveyed flows. This space is usually designed as a pipe with preferably cylindrical geometry, wherein the geometry may also differ from the cylindrical geometry and, for example, may be configured spherical.

In a preferred embodiment, the valve body is arranged vertically or vertically, i. the axis, which can be placed through the delivery valves and the space between the delivery valves, is vertical.

The delivery valves are spatially separated from the positive displacement pump by a transfer line.
The pendulum line preferably has an "L" -shaped geometry, ie the pendulum line has in this geometry an area which extends horizontally and a part which extends vertically. Deviations from this geometry are possible, for example, to allow a connection between positive displacement pump and valve body, if the arrangement of positive displacement pump and valve body due to structural conditions does not allow a strictly 'L''- shaped geometry.
If the valve body is arranged vertically, then usually the horizontal part of the shuttle leads into the valve housing into the cavity between the two delivery valves. The adjoining the horizontal part of the pendulum line vertical region of the pendulum line is usually connected directly or via another area of the pendulum line, which does not necessarily have to be arranged vertically, with the pump chamber of the positive displacement pump.
If the valve body is arranged horizontally, usually the vertical part of the shuttle leads into the cavity of the valve body between the two delivery valves. The adjoining the vertical part of the pendulum line horizontal region of the pendulum line is usually connected directly or via another area of the pendulum line, which does not necessarily have to be arranged horizontally, with the pump chamber of the positive displacement pump.

In a preferred embodiment, the part of the pendulum line, which is connected to the valve body, and the valve body itself are heated to a temperature above the melting temperature or above the saturation temperature of the liquid to be delivered. The heating of the heated part of the pendulum line and the valve housing can usually be done with steam or heat transfer oil.

The heated part of the pendulum line is preferably so large that, together with the cavity in the valve body between the two delivery valves at least one volume is included, which is about 3 to 20 times, preferably 5 to 15 times and more preferably 7 to 12 times the displacement of the positive displacement pump corresponds. Thus, it is generally ensured that the fluid to be delivered comes into contact only with the heated part of the shuttle.
The shuttle line is connected to the pressure side of a positive displacement pump ("main pump").
Preferably, the positive displacement pump ("main pump") is a piston pump or a diaphragm pump, with a diaphragm pump being particularly preferred since it has no Sealing and lubricants needed that could contaminate the liquid to be pumped.
Suitable membrane materials are elastomeric materials such as ethylene-propylene-diene rubber (EPDM), silicone rubber (MVO, VMO), fluoro-silicone rubber (MFO, FVMO), fluoro rubber (FPM, FKM), perfluoro rubber (FFKM, FFPM), polychloroprene rubber (CR), nitrile butadiene rubber (NBR), polyester urethane rubber (AU, EU), butyl rubber (IIR) and natural rubber (NR). It is also possible to use polymer membranes made of polytetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene (PP) or other plastic membranes which are chemically resistant to the auxiliary liquid used. It is also possible to use coated membranes such as PTFE-coated elastomeric membranes or multi-layer membranes made of different materials.
Preferred membrane materials are polytetrafluoroethylene (PTFE) and polyethylene (PE), wherein the use of PTFE and PTFE-coated elastomer membranes as membrane material for promoting aromatic compounds and carboxylic acids or carboxylic acid derivatives are particularly preferred.

The main pump is connected on the suction side with a pipe ("connecting line") through which auxiliary liquid can be supplied.
The supply of the auxiliary liquid through the connecting line is preferably carried out by a further positive displacement pump ("auxiliary pump").
The auxiliary pump is a positive displacement pump, which is preferably designed as a piston or diaphragm pump, particularly preferably as a diaphragm pump. Suitable membrane materials are the aforementioned materials, such as PTFE and PTFE-coated membranes, which are resistant to the respective auxiliary liquid.

In the connecting line, a check valve is preferably attached, which prevents liquid from the main pump can flow in the direction of the auxiliary pump.
Between the check valve and the main pump is usually a valve for venting the pump chamber of the main pump. This valve is generally mounted at the highest point of the pump system to allow complete venting.
In general, delivery valves are attached to the suction and delivery side directly on the pump head of the auxiliary pump.
The delivery valves are generally designed so that the fluid to be delivered can pass the valves only from the suction side in the direction of the pressure side. The flow in the opposite direction (from the pressure side to the suction side) is generally blocked. For example, the valves can be designed as check valves, preferably ball check valves.

At the highest point between the delivery valve on the pressure side and the check valve in the connecting line usually another valve is attached, which serves to vent this part of the pipeline.
The suction side of the auxiliary pump is connected to a reservoir, for example a container or a tank in which the auxiliary liquid is located.
The auxiliary liquid can be heated prior to introduction into the pump space of the auxiliary pump, for example by a heat exchanger or by heating the receiver tank, wherein the temperature should not be so high that neither the main nor the auxiliary pump, in particular the membrane material of a diaphragm pump, is damaged.

The pendulum line is usually filled with liquid.
Preferably, the pendulum line and the space within the valve body, which is located between the delivery valves, before the start of the process according to the invention for the delivery of liquids - ie before the start of the pumping operation - completely or almost completely filled with auxiliary fluid. It is advantageous if at least the non-heated part of the pendulum line is filled with auxiliary liquid, since the auxiliary liquid has a lower melting point than the liquid to be conveyed and does not or does not need to be heated so much to remain liquid. Thus, the formation of deposits of solids in the pump system can be further reduced.

To initiate the delivery process, the auxiliary liquid in the main pump and the valve body is initially pumped out by a lifting movement of the main pump (delivery) from the pump system. The delivery valve in the valve body on the suction side prevents backflow in the direction of the reservoir tank of the liquid to be conveyed and the check valve in the connecting line prevents auxiliary fluid pumped out of the main pump from flowing back to the auxiliary pump.

By a suction stroke of the main pump, the liquid to be conveyed is conveyed through the supply line on the suction side into the valve body and partly into the transfer line.
In this case, the liquid to be conveyed usually does not reach the entire part of the transfer line, since the auxiliary liquid usually forms approximately a liquid barrier, which hinders the propagation of the liquid to be conveyed in the pendulum line. Thus, it is generally ensured that the displacement pump, in particular also the diaphragm of a diaphragm pump, does not come into contact with the fluid to be delivered, but is generally surrounded by the auxiliary fluid.

However, as a rule, the auxiliary liquid does not form an ideal liquid barrier, so that part of the liquid to be conveyed mixes with the auxiliary liquid and diffuses in the direction of the main pump, for example when a high temperature gradient occurs between the heated valve body and the pump head of the main pump. Due to the diffusion of the liquid to be conveyed, deposits may occur in the region of the main pump and the unheated part of the transfer line.

In order to reduce the formation of these deposits in the region of the unheated parts of the pump system, according to the invention auxiliary liquid is introduced into the commutation line. The introduction of the auxiliary liquid causes a flow towards the valve body of the main pump, which generally counteracts the propagation of the liquid to be conveyed by convection or diffusion.
The introduction is preferably carried out continuously.
In a preferred embodiment, the auxiliary liquid is introduced by means of a positive displacement pump ("auxiliary pump") through the connecting line into the pump chamber of the main pump. A check valve in the connection line generally causes the liquid to flow only in the direction of the main pump.
The volume flow of the auxiliary liquid to the volume flow of the liquid to be conveyed is preferably in the range of 1: 100 to 1:10, more preferably in the range of 1:80 to 2:10, particularly preferably 1:50 to 5:10.

By oscillating movements of the main pump, the conveying and suction strokes are repeatedly carried out, wherein the pumping movement is transmitted by the auxiliary liquid to the liquid to be conveyed, so that the liquid to be conveyed can be continuously conveyed through the inlet of the valve body in the direction of outlet.

In a preferred embodiment, the lift linkage of the main pump and the auxiliary pump are mechanically coupled together. The mechanical coupling is designed so that the auxiliary pump is exactly in the delivery stroke when the main pump is in the suction stroke and vice versa. However, it is also possible to drive the two pumps by means of separate drives and to carry out the synchronization of the strokes by electronic means, such as by means of variable frequency converters.

Since the pump head of the main pump, in particular the diaphragm of a diaphragm pump, and the majority of the transfer line usually comes into contact only with the auxiliary liquid, the temperature can be set lower in this area, since it is only necessary that the temperature in the pump head and in the non-heated part of the shuttle is so high that the auxiliary liquid remains in a liquid state and the formation of deposits is largely avoided. In a preferred embodiment, the pump head of the main pump and the unheated part of the transfer line is not additionally heated and uses an auxiliary liquid having a melting point below the ambient temperature. This embodiment allows a particularly economical embodiment of the pump system. However, in order to reduce the temperature difference between the auxiliary liquid and the liquid to be conveyed, for example, to reduce the diffusion of the liquid to be conveyed into the auxiliary liquid, the auxiliary liquid may be heated before being introduced into the pump space of the auxiliary pump as described above.

The geometric arrangement of the pump system is generally carried out depending on the substances to be conveyed. When the density of the liquid to be delivered is higher than the density of the auxiliary liquid, in each case at the operating temperatures, the valve body is usually arranged lower than the main pump. Accordingly, the valve body is usually arranged above the main pump when the liquid to be conveyed has a lower density than the auxiliary liquid.

• In Fig. 1 ist das erfindungsgemäße Pendel-Pumpensystem für Schmelzen schematisch dargestellt. Dabei ist (1) der Zulauf der Schmelze (Saugseite) und (2) stellt den Abzug der Schmelze (Druckseite) zum chemischen Verfahren dar. Der Ventilkörper (6) besitzt Ventile auf der Saugseite (10) und auf der Druckseite (11) der Schmelze, welche nur in Strömungsrichtung von (1) nach (2) Flüssigkeit passieren lassen, in Gegenrichtung jedoch blockieren.

Zwischen den Ventilen (10) und (11) ist eine Rohrleitung angebracht, die so genannte Pendelleitung (7), welche vollständig mit Flüssigkeit gefüllt ist. Der Ventilkörper (6) sowie der untere Teil der Pendelleitung (7) sind mit einem Heizmedium wie beispielsweise Dampf oder Wärmeträgeröl beheizt, um ein Festwerden der Schmelze im Ventilkörper oder in der Pendelleitung zu verhindern. Die Positionen (8) und (9) zeigen Zugang sowie Abgang des Heizmediums.
Die Pendelleitung (7) ist mit der Haupt-Membranpumpe (12) verbunden. Die Membran wird über einen Motor mit Getriebe (17) über ein Hubgestänge angetrieben. Die Membranpumpe (12) ist mit einer zweiten Rohrleitung (Verbindungsleitung) (5) zur Dosierung von Hilfsflüssigkeit verbunden. In dieser Zuführung für die Hilfsflüssigkeit ist ein Rückschlagventil (14) angebracht, mit welcher verhindert wird, dass Flüssigkeit von der Hauptpumpe (12) in Richtung Hilfspumpe (16) strömen dann. Zwischen Rückschlagventil (14) und Membranpumpe (12) befindet sich am höchsten Punkt ein Ventil (13) zum vollständigen Entlüften des Pumpenraumes (5), (12), (7).
Die Hilfsflüssigkeit wird mittels einer kleinen Membran-Dosierpumpe, der Hilfspumpe (16), der Hauptpumpe (12) zugeführt. Dabei ist (3) die Zuführung der Hilfsflüssigkeit (Saugseite) zur Hilfspumpe (16) und Anschluss (4) stellt die Druckseite der Hilfspumpe dar. Bei dieser Hilfspumpe (16) sind die Förderventile (18) und (19) direkt am Membranpumpenkopf an Saug- und Druckseite angebracht. An der höchsten Stelle der Verbindungsleitung zwischen Druckseite der Hilfsflüssigkeit und dem Rückschlagventil (14) befindet sich ein Ventil (15) zum vollständigen Entlüften dieser Rohrleitung. Die Hilfspumpe (16) wird mechanisch mittels Elektromotor und Getriebe (17) über ein Hubgestänge angetrieben. In dieser bevorzugten Ausführungsform sind das Hubgestänge der Hauptpumpe (12) und der Hilfspumpe (16) mechanisch miteinander gekoppelt. Die mechanische Koppelung ist dabei so ausgeführt, dass die Hilfspumpe (16) sich genau dann im Förderhub befindet, wenn sich die Hauptpumpe (12) im Saughub befindet und umgekehrt.With reference to the accompanying schematic drawing ( FIG. 1 ), but not by way of limitation thereto, a preferred embodiment of the method according to the invention for the conveyance of liquids is described below:

• In Fig. 1 the inventive pendulum pump system for melting is shown schematically. Here, (1) is the inflow of the melt (suction side) and (2) represents the withdrawal of the melt (pressure side) to the chemical process. The valve body (6) has valves on the suction side (10) and on the pressure side (11) Melt, which allow liquid to pass only in the flow direction from (1) to (2), but block in the opposite direction.

Between the valves (10) and (11) a pipe is attached, the so-called pendulum line (7), which is completely filled with liquid. The valve body (6) and the lower part of the pendulum line (7) are heated with a heating medium such as steam or heat transfer oil to prevent solidification of the melt in the valve body or in the pendulum line. The positions (8) and (9) show access and outlet of the heating medium.
The shuttle (7) is connected to the main diaphragm pump (12). The membrane is driven via a motor with gear (17) via a lifting linkage. The diaphragm pump (12) is connected to a second pipeline (connecting line) (5) for metering auxiliary liquid. In this supply for the auxiliary liquid, a check valve (14) is mounted, with which prevents liquid from the main pump (12) in the direction of the auxiliary pump (16) then flow. Between check valve (14) and diaphragm pump (12) is located at the highest point a valve (13) for completely venting the pump chamber (5), (12), (7).
The auxiliary liquid is supplied by means of a small diaphragm metering pump, the auxiliary pump (16), the main pump (12). In this case, (3) the supply of the auxiliary liquid (suction side) to the auxiliary pump (16) and port (4) provides the pressure side of the auxiliary pump In this auxiliary pump (16), the delivery valves (18) and (19) are attached directly to the diaphragm pump head on suction and pressure side. At the highest point of the connecting line between the pressure side of the auxiliary liquid and the check valve (14) is a valve (15) for completely venting this pipeline. The auxiliary pump (16) is mechanically driven by means of electric motor and gear (17) via a lifting linkage. In this preferred embodiment, the lift linkage of the main pump (12) and the auxiliary pump (16) are mechanically coupled together. The mechanical coupling is designed so that the auxiliary pump (16) is exactly in the delivery stroke when the main pump (12) is in the suction stroke and vice versa.

With the method according to the invention, liquids which are used as starting materials in a chemical reaction can be conveyed.

With the method according to the invention, for example, feedstocks for reactions such as hydrogenations, oxidation, esterifications and polymerizations can be promoted in a chemical reactor.

The starting material can be used as a melt or as a concentrated solution of the starting material.
The liquid to be conveyed is particularly preferably used as a melt, particularly preferably as a melt of the commercially available pure substance.
The use of a melt generally has the advantage that the compound to be conveyed does not have to be dissolved in a separate process step in order to obtain a recoverable liquid. The feedstock is also not diluted by a solvent, so that the reactor can usually be charged with a higher amount of starting material and a complicated separation of the solvent after completion of the reaction is generally not required.
The starting material can also be used as a solution of the starting material.
The solvent used for the starting material is generally the solvent, which is preferably used in the corresponding process or in the respective reaction. This embodiment is advantageous, for example, if the starting materials tend to discolour or to give secondary reactions during melting. By preparing a concentrated solution of the feedstock, the temperature for transferring the feedstock to the liquid state can be lowered. In order to achieve the highest possible reactor utilization, a solution which is as concentrated as possible is generally prepared. By means of the method according to the invention, it is possible to deliver concentrated solutions having a high saturation temperature, since continuous feeding of auxiliary liquid can largely prevent the concentrated solution from reaching the region of the pump head of the main pump.

For this reason, it is also possible to use the feedstock as a slurry in the auxiliary liquid. Thus, the inventive method is also suitable for the promotion of non-meltable starting materials, such as terephthalic acid, for example, to promote a slurries of the starting material terephthalic acid in ethylene glycol.

With particular preference, melts having a melting point of 20 ° C. or more, preferably 50 ° C. or more, particularly preferably 75 ° C. or more and very particularly preferably 100 ° C. or more, can be conveyed by means of the process according to the invention.
Furthermore, solutions of a starting material may preferably be promoted, wherein the saturation temperature of the solution at a temperature of 20 ° C or more, preferably 50 ° C or more, more preferably at 75 ° C or more, and most preferably 100 ° C or more ,
The saturation temperature is understood to be the temperature at which a solution of a starting material, with a certain concentration, reaches the saturation state and the starting material begins to precipitate out of the solution.

The temperature at which the liquid to be conveyed is conveyed is above its melting temperature or above its saturation temperature.
Preferably, the conveying temperature is 1 ° C to 100 ° C, preferably 5 ° C to 80 ° C and more preferably 10 ° to 50 ° C above the melting temperature or the saturation temperature of the liquid to be conveyed.

In general, the temperature of the liquid to be conveyed should not exceed 300.degree. C., preferably not more than 250.degree. C., and more preferably not more than 200.degree. Since the temperature of the auxiliary liquid in the region of the pump head is usually limited by the temperature resistance of the membrane, as described below, a high temperature gradient between valve body and pump chamber can lead to increased mixing between the liquid to be conveyed and the auxiliary liquid. As a rule, the ratio of the volume flow of the auxiliary liquid to the volume flow of the fluid to be conveyed should be higher, the higher the temperature gradient between the valve body and the pump chamber.

The auxiliary liquid according to the invention is a product of the chemical reaction or an educt of the chemical reaction.
If a product of the chemical reaction is used as the auxiliary liquid, preferably the main product is used as the auxiliary liquid which preferably forms under the conditions of the respective chemical reaction.
The fact that either an educt or a product of the chemical reaction is used as the auxiliary liquid, it is prevented that the liquid to be conveyed is contaminated by foreign matter.

The melting point of the auxiliary liquid according to the invention is below the melting temperature or below the saturation temperature of the liquid to be conveyed.
In a particular embodiment, the melting point of the auxiliary liquid is below the temperature at which the membrane of a membrane pump is stable, so that the membrane is not thermally damaged.
In a particularly preferred embodiment, the melting temperature of the auxiliary liquid is 150 ° C or less, more preferably 100 ° C or less, even more preferably 50 ° C or less, and most preferably 25 ° C or less. At these temperatures, safe operation of diaphragm pumps is usually possible.

The temperature at which the auxiliary liquid is introduced into the connecting line is above its melting temperature.
Preferably, the temperature at which the auxiliary liquid is introduced into the connecting line 1 ° C to 100 ° C, preferably 5 ° C to 80 ° C and more preferably 10 ° to 50 ° C above the melting temperature of the auxiliary liquid.
Most preferably, the temperature at which the auxiliary liquid is introduced into the connecting line is in the range of 0 ° C to 150 ° C, preferably in the range of 10 ° C to 100 ° C, more preferably in the range of 20 ° C to 80 ° C. particularly preferably in the range from 20 ° C to 50 ° C.

The boiling point of the auxiliary liquid should preferably be above the conveying temperature of the liquid to be conveyed, since otherwise undesired gas formation may occur at the interface of the auxiliary liquid and the liquid to be conveyed in the region of the commutation line.

• aromatische Amine, wie Anilin, Benzidin, die isomeren Touidine, die isomeren Xylidine, die isomeren Xylylendiamine, 1- bzw. 2-Aminonaphthalin, TDA-Isomere (2,4/2,6/2,3/3,4-Toluoldiamin) oder MDA-Isomere (4,4'- Methylendianilin, 2,4'- Methylendianilin, 2,2'- Methylendianilin, polymer-MDA) sowie von Mischungen derselben;
• substituierte MDA-Verbindungen, wie 3,3'-Dimethyl-4,4'-diaminodiphenylmethan, 3,3',5,5'-Tetramethyl-4,4'-diaminodiphenylmethan und 2,2',3,3'-Tetramethyl-4,4'-diaminodiphenylmethan;
• aromatische Dinitrile, wie die isomeren Phthalodinitrile;
• aromatische Hydroxyverbindungen, wie Bisphenol-A, Bisphenol-F oder substituierte Bisphenole;
• aromatische Säureanhydride, wie Phthalsäureanhydrid; oder
• aromatischen Säuren, wie Benzoesäure.

Besonders bevorzugt werden aromatische Amine als Einsatzstoffe in eine Hydrierung gefördert.
Zur Förderung von aromatischen Einsatzstoffen wird gemäß der hier beschriebenen Ausführungsform das Produkt der Hydrierung des aromatischen Einsatzstoffes als Hilfsflüssigkeit eingesetzt. Für den Fall, dass bei der Hydrierung der aromatischen Einsatzstoffe mehrere Hydrierungsprodukte entstehen können, wird bevorzugt das Hydrierungsprodukte eingesetzt, das bei den jeweiligen Reaktionsbedingungen das Hauptprodukt darstellt. Beispielsweise kann zur Förderung von 2,4-Toluoldiamin 2,4Diamino-1-methyl-cyclohexan als Hilfsflüssigkeit eingesetzt werden.In a preferred embodiment, the auxiliary liquid is a product of the chemical reaction.
This particularly preferred embodiment is preferably suitable for promoting an aromatic compound which is used as starting material for a hydrogenation.
Preferred starting materials are:

• aromatic amines, such as aniline, benzidine, the isomeric togidines, the isomeric xylidines, the isomeric xylylenediamines, 1- or 2-aminonaphthalene, TDA isomers (2,4 / 2,6 / 2,3 / 3,4-toluenediamine) or MDA isomers (4,4'-methylenedianiline, 2,4'-methylenedianiline, 2,2'-methylenedianiline, polymeric MDA) and mixtures thereof;
• substituted MDA compounds such as 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane and 2,2', 3,3'-tetramethyl 4,4'-diaminodiphenylmethane;
• aromatic dinitriles, such as the isomeric phthalodinitriles;
• aromatic hydroxy compounds such as bisphenol A, bisphenol F or substituted bisphenols;
• aromatic acid anhydrides such as phthalic anhydride; or
• aromatic acids, such as benzoic acid.

Particularly preferred aromatic amines are promoted as starting materials in a hydrogenation.
For the promotion of aromatic starting materials, the product of the hydrogenation of the aromatic starting material is used as an auxiliary liquid according to the embodiment described herein. In the event that several hydrogenation products can be formed in the hydrogenation of the aromatic feedstocks, the hydrogenation product which is the main product under the particular reaction conditions is preferably used. For example, 2,4-diamino-1-methyl-cyclohexane can be used as an auxiliary liquid to promote 2,4-toluenediamine.

The particularly preferred embodiment, in which a product of the chemical reaction is used as auxiliary liquid, is also suitable for the promotion of carboxylic acids or carboxylic acid derivatives in the preparation of esters or polyesters.

• aromatische Carbonsäuren, wie Benzoesäure, insbesondere aromatische Dicarbonsäuren, wie Phthalsäure, Isophthalsäure, Terephthalsäure oder die isomeren Naphthalindicarbonsäuren; oder
• aliphatische Carbonsäuren, insbesondere aliphatische Dicarbonsäuren, wie Adipinsäure, Bernsteinsäure, Glutarsäure, Korksäure, Azelainsäure, Sebacinsäure, Decandicarbonsäure, Maleinsäure oder Fumarsäure

Die Carbonsäuren können dabei sowohl einzeln als auch im Gemisch untereinander verwendet werden.Preferred carboxylic acids are:

• aromatic carboxylic acids, such as benzoic acid, in particular aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid or the isomeric naphthalenedicarboxylic acids; or
• aliphatic carboxylic acids, in particular aliphatic dicarboxylic acids, such as adipic acid, succinic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid or fumaric acid

The carboxylic acids can be used both individually and in admixture with each other.

In this preferred embodiment, the corresponding carboxylic acid derivatives of carboxylic acids, for example the corresponding carboxylic anhydrides or their esters, for example the C ₁ -C ₄ esters of the abovementioned carboxylic acids, can also be used as starting materials. Preferably, the corresponding carboxylic acid anhydrides of the abovementioned carboxylic acids, in particular phthalic anhydride, maleic anhydride or succinic anhydride, are used.
In the esterification of carboxylic acids or carboxylic acid derivatives with alcohols, according to the embodiment described here, an ester of carboxylic acid and alcohol is used as an auxiliary liquid for promoting the carboxylic acid or the carboxylic acid derivative.
For example, methyl benzoate can be used as an auxiliary liquid for the promotion of benzoic acid in the preparation of benzoic acid methyl ester from benzoic acid and methanol.

By using the product obtained in the chemical reaction of the starting material as an auxiliary liquid to promote the feedstock, there is none unwanted contamination of the liquid to be pumped with foreign substances. Furthermore, there are no additional costs for cleaning the final product of, for example, a solvent.

In a further preferred embodiment, the auxiliary liquid in the process according to the invention for conveying a liquid is an educt of the chemical reaction.
By means of this particularly preferred embodiment, it is preferred to promote carboxylic acids or carboxylic acid derivatives which are used as starting materials for esterification.

• aromatische Carbonsäuren, wie Benzoesäure, insbesondere aromatische Dicarbonsäuren, wie Phthalsäure, Isophthalsäure, Terephthalsäure oder die isomeren Naphthalindicarbonsäuren; oder
• aliphatische Carbonsäuren, insbesondere aliphatische Dicarbonsäuren, wie Adipinsäure, Bernsteinsäure, Glutarsäure, Korksäure, Azelainsäure, Sebacinsäure, Decandicarbonsäure, Maleinsäure oder Fumarsäure.

Die Carbonsäuren können dabei sowohl einzeln als auch im Gemisch untereinander verwendet werden.Preferred carboxylic acids are:

• aromatic carboxylic acids, such as benzoic acid, in particular aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid or the isomeric naphthalenedicarboxylic acids; or
• aliphatic carboxylic acids, in particular aliphatic dicarboxylic acids, such as adipic acid, succinic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid or fumaric acid.

The carboxylic acids can be used both individually and in admixture with each other.

In this embodiment, the corresponding carboxylic acid derivatives of carboxylic acids, for example the corresponding carboxylic anhydrides or their esters, for example the C ₁ -C ₄ esters of the abovementioned carboxylic acids, can also be used as starting materials. Preferably, the corresponding carboxylic acid anhydrides of the abovementioned carboxylic acids, in particular phthalic anhydride, maleic anhydride or succinic anhydride, are used.
In this embodiment, an educt of the chemical reaction is used as the auxiliary liquid.
In the promotion of carboxylic acids or carboxylic acid derivatives which are used as starting materials in an esterification, the auxiliary liquid according to the invention is an alcohol with which the carboxylic acid or the carboxylic acid derivative is to be reacted.

• aliphatische Alkohole, wie C₁- bis C₂₀-Alkohole, bevorzugt C₁- bis C₄-Alkohole, wie Methanol, Ethanol, die isomeren Propanole oder die isomeren Butanole; 2-Ethylhexanol,
• aliphatische Diole, wie C₂- bis C₂₀-Diole, vorzugsweise 1,2-Ethandiol, 1,3-Propandiol, 1,2-Propandiol, 1,4-Butandiol, 1,5-Pentandiol, 1,6-Hexandiol, Cyclohexandiol oder Neopentylglykol;
• aliphatische Polyole, wie Trimethylolpropan, Trimethylolethan, Pentaerythrit, Glycerin und Poly-Tetrahydrofuran;
• cycloaliphatische Polyole wie Mono- und Di- und Oligosaccharide und deren wässrige Lösungen; oder
• Zuckeralkohole, wie Sorbitol, Glucitol oder Hexanhexol und deren wässrige Lösungen. Die Alkohole können dabei sowohl einzeln als auch im Gemisch untereinander verwendet werden, in Abhängigkeit davon welcher Ester bzw. Polyester hergestellt werden soll.

As alcohol can be used for example:

• aliphatic alcohols, such as C ₁ - to C ₂₀ -alcohols, preferably C ₁ - to C ₄ -alcohols, such as methanol, ethanol, the isomeric propanols or the isomeric butanols; 2-ethylhexanol,
• aliphatic diols, such as C ₂ - to C ₂₀ -diols, preferably 1,2-ethanediol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, Cyclohexanediol or neopentyl glycol;
• aliphatic polyols such as trimethylolpropane, trimethylolethane, pentaerythritol, glycerol and poly-tetrahydrofuran;
• cycloaliphatic polyols such as mono- and di- and oligosaccharides and their aqueous solutions; or
• Sugar alcohols such as sorbitol, glucitol or hexanehexol and their aqueous solutions. The alcohols can be used both individually and in admixture with one another, depending on which ester or polyester is to be produced.

As described above, the process according to the invention will preferably be used to promote aromatic compounds used in a hydrogenation.
Accordingly, the present invention relates to a process for the hydrogenation of aromatic compounds, characterized in that an aromatic compound or a solution of an aromatic compound by means of a positive displacement pump with spatially separated delivery valves and a liquid-filled transfer line between the positive displacement pump and delivery valves to the reactor, wherein in the Pendulum is an auxiliary liquid which is the product of the hydrogenation of the aromatic compound and wherein the auxiliary liquid has a melting point which is below the melting point of the aromatic compound or below the saturation temperature of the solution of the aromatic compound.
The hydrogenation is usually carried out at suitable pressures and temperatures. The temperature is generally in the range of 50 and 300 ° C, the temperature range of 120 to 280 ° C is preferred, and the pressure is usually from 1 to 500 bar, preferably from 50 to 325 bar, particularly preferably from 150 to 250 bar.
The hydrogenation process can be carried out continuously or in the manner of a batch process.
With continuous process control, the amount of compound or compounds for hydrogenation is preferably about 0.01 to about 3 kg per liter of catalyst per hour, more preferably about 0.05 to about 1 kg per liter of catalyst per hour.
As the hydrogenation gases, any gases containing hydrogen and having no harmful amounts of catalyst poisons such as CO may be used. For example, reformer exhaust gases can be used. Preferably, pure hydrogen is used as the hydrogenation gas.
The hydrogenation is usually carried out in the presence of a homogeneous or heterogeneous catalyst which is suitable for hydrogenations. Preferably, the hydrogenation is carried out in the presence of a heterogeneous catalyst.
Suitable homogeneous catalysts are liquid and / or soluble hydrogenation catalysts, for example Wilkinson catalysts, Crabtree catalysts or Lindlar catalysts.
As heterogeneous catalysts, for example, noble metals such as platinum, palladium, ruthenium, osmium, iridium and rhodium or other transition metals such Molybdenum, tungsten, chromium, but especially iron, cobalt and nickel, either singly or in admixture. The catalyst metals can be used directly in the form of the metal or an inorganic metal compound or the catalyst metals are applied to an inert, inorganic support material such as alumina, SiO ₂ , TiO ₂ and activated carbon.
The hydrogenation can be carried out without solvent or in the presence of a solvent. As the solvent, alcohols such as methanol, ethanol, propanol, isopropanol, isobutanol or t-butanol, or ethers such as diethyl ether, glycol dimethyl ether, dioxane or tetrahydrofuran can be used. As a solvent, however, it is also possible to use the end product formed during the reaction. Suitable solvents are also mixtures of the abovementioned solvents.
The following aromatic compounds are preferably used in the process of the invention for the hydrogenation of aromatic compounds.

• aromatische Amine, wie Anilin, Benzidin, die isomeren Touidine, die isomeren Xylidine, die isomeren Xylylendiamine, 1- bzw. 2-Aminonaphthalin, TDA-Isomere (2,4/2,6/2,3/3,4-Toluoldiamin) oder MDA-Isomere (4,4'- Methylendianilin, 2,4'- Methylendianilin, 2,2'- Methylendianilin, polymer-MDA) sowie von Mischungen derselben;
• substituierte MDA-Verbindungen, wie 3,3'-Dimethyl-4,4'-diaminodiphenylmethan, 3,3',5,5'-Tetramethyl-4,4'-diaminodiphenylmethan und 2,2',3,3'-Tetramethyl-4,4'-diaminodiphenylmethan;
• aromatische Dinitrile, wie die isomeren Phthalodinitrile;
• aromatische Hydroxyverbindungen, wie Bisphenol-A, Bisphenol-F oder substituierte Bisphenole;
• aromatische Säureanhydride, wie Phthalsäureanhydrid; oder
• aromatischen Säuren, wie Benzoesäure.
• Besonders bevorzugt werden aromatische Amine als Einsatzstoffe in eine Hydrierung gefördert. Ein Verfahren zur Hydrierung von aromatischen Aminen ist beispielsweise in der DE-A1-2132547 offenbart.

Als Hilfsflüssigkeit wird erfindungsgemäß das Produkt der Hydrierung der aromatischen Verbindung eingesetzt. Vorzugsweise wird das Hauptprodukt als Hilfsflüssigkeit eingesetzt, das unter den Bedingungen der Hydrierung bevorzugt entsteht.Preferred starting materials are:

• aromatic amines, such as aniline, benzidine, the isomeric togidines, the isomeric xylidines, the isomeric xylylenediamines, 1- or 2-aminonaphthalene, TDA isomers (2,4 / 2,6 / 2,3 / 3,4-toluenediamine) or MDA isomers (4,4'-methylenedianiline, 2,4'-methylenedianiline, 2,2'-methylenedianiline, polymeric MDA) and mixtures thereof;
• substituted MDA compounds such as 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane and 2,2', 3,3'-tetramethyl 4,4'-diaminodiphenylmethane;
• aromatic dinitriles, such as the isomeric phthalodinitriles;
• aromatic hydroxy compounds such as bisphenol A, bisphenol F or substituted bisphenols;
• aromatic acid anhydrides such as phthalic anhydride; or
• aromatic acids, such as benzoic acid.
• Particularly preferred aromatic amines are promoted as starting materials in a hydrogenation. A process for the hydrogenation of aromatic amines is for example in the DE-A1-2132547 disclosed.

As auxiliary liquid, the product of the hydrogenation of the aromatic compound is used according to the invention. Preferably, the main product is used as an auxiliary liquid, which preferably arises under the conditions of the hydrogenation.

The process according to the invention is, as explained above, also preferably suitable for the extraction of carboxylic acids or carboxylic acid derivatives which are used in a process for the preparation of esters or polyesters, for example by esterification or transesterification.

Accordingly, the present invention relates to a process for the preparation of esters, characterized in that supplying a carboxylic acid or a carboxylic acid derivative or a solution of a carboxylic acid or a carboxylic acid derivative by means of a positive displacement pump with spatially separated delivery valves and a liquid-filled transfer line between the positive displacement pump and delivery valves to the reactor the auxiliary line is an auxiliary liquid which is the product of ester production or an alcohol used as starting material and wherein the auxiliary liquid has a melting point below the melting point of the carboxylic acid or of the carboxylic acid derivative or below the saturation temperature of the solution of the carboxylic acid or Carboxylic acid derivative is located.
For the preparation of the esters, such as in Ullmann's Encyclopedia of Industrial Chemistry, Polyesters (Electronic Release DOI : 10.1002 / 14356007.a21_227), the abovementioned carboxylic acids or carboxylic acid derivatives and the abovementioned alcohols catalyst-free or preferably in the presence of esterification catalysts, advantageously in an atmosphere of inert gases, such as. B. nitrogen, carbon monoxide, helium, argon and others in the melt at temperatures of 150 to 250 ° C, preferably 180 to 220 ° C optionally under reduced pressure to the desired acid number, which is advantageously less than 10, preferably less than 2, be condensed.
For the preparation of polyester polyols, the organic polycarboxylic acids and / or derivatives and polyhydric alcohols are advantageously used in a molar ratio of 1: 1 to 1.8, preferably 1: 1.05 to 1.2.
As catalysts it is possible to use basic or acidic catalysts, preferably acidic catalysts, such as toluenesulfonic acids, preferably organometallic compounds, in particular those based on titanium or tin, such as titanium tetrabutoxide or tin (II) octoate.

• aromatische Carbonsäuren, wie Benzoesäure, insbesondere aromatische Dicarbonsäuren, wie Phthalsäure, Isophthalsäure, Terephthalsäure oder die isomeren Naphthalindicarbonsäuren; oder
• aliphatische Carbonsäuren, insbesondere aliphatische Dicarbonsäuren, wie Adipinsäure, Bernsteinsäure, Glutarsäure, Korksäure, Azelainsäure, Sebacinsäure, Decandicarbonsäure, Maleinsäure oder Fumarsäure.

Die Carbonsäuren können dabei sowohl einzeln als auch im Gemisch untereinander verwendet werden.
In dieser Ausführungsform können auch die entsprechenden Carbonsäurederivate von Carbonsäuren, beispielsweise die entsprechenden Carbonsäureanhydride oder deren Ester, beispielsweise die C₁-C₄-Ester der oben genannten Carbonsäuren, als Einsatzstoffe eingesetzt werden. Vorzugsweise werden die entsprechenden Carbonsäureanhydride der obengenannten Carbonsäuren, insbesondere Phthalsäureanhydrid, Maleinsäureanhydrid oder Bernsteinsäureanhydrid, eingesetzt.Preferred carboxylic acids are:

• aromatic carboxylic acids, such as benzoic acid, in particular aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid or the isomeric naphthalenedicarboxylic acids; or
• aliphatic carboxylic acids, in particular aliphatic dicarboxylic acids, such as adipic acid, succinic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid or fumaric acid.

The carboxylic acids can be used both individually and in admixture with each other.
In this embodiment, the corresponding carboxylic acid derivatives of carboxylic acids, for example the corresponding carboxylic anhydrides or their esters, for example the C ₁ -C ₄ esters of the abovementioned carboxylic acids, can also be used as starting materials. Preferably, the corresponding carboxylic acid anhydrides of the abovementioned carboxylic acids, in particular phthalic anhydride, maleic anhydride or succinic anhydride, are used.

The auxiliary liquid used according to the invention is the product of ester production or an alcohol which is used as starting material in the preparation of the ester.

The process according to the invention is particularly suitable for promoting compounds which have a high melting point or which are in the form of concentrated solutions and have a high saturation temperature. Such substances can - due to the high melting point or its high saturation temperature - form deposits at insufficiently heated points of the feed pump. However, the heating of feed pumps proves to be technically complex, since on the one hand not all conventional materials that are used for the construction of pumps are thermally stable, in particular membranes and seals. Thus, the production of high temperature pumps is relatively expensive, despite sacrificing performance compared to conventional pumps that can be operated at ambient temperature.
With the aid of the method according to the invention, high-melting compounds or highly concentrated solutions can be conveyed with conventional pumps, the tendency for the formation of deposits in the area of the pump system being reduced. This allows a long service life with long intervals between the maintenance intervals. Furthermore, the wear of the pumps is reduced, so that the life is increased.
Another advantage is that the reaction mixture is not contaminated by non-reactive substances that would otherwise have to be separated from the desired product in complex steps.

The invention is further illustrated by the following examples.

Examples Example 1: Hydrogenation of Toluene Diamine to Cycloaliphatic Diamines

Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C 2,4-toluenediamine (TDA) 97 2,4-diamino-1-methyl-cyclohexane <0 2,6-toluenediamine (TDA) 104 2,6-diamino-1-methyl-cyclohexane <0

Example 2: Hydrogenation of optionally substituted MDA to cycloaliphatic amines

R1 R2 Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C H H 4,4'-methylenedianiline (MDA) 89 4,4'-diaminodicyclohexylmethane (PACM50) 45 4,4'-diaminodicyclohexylmethane (PACM20) 15 CH ₃ H 3,3'-dimethyl-4,4'-diaminodiphenylmethane 159 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane <0 CH ₃ CH ₃ 3,3 ', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane 121 3,3 ', 5,5'-tetramethyl-4,4'-diaminodicyclohexylmethane <0

Example 3: Hydrogenation of aromatic dinitriles to cycloaliphatic diamines

Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C m-Phthalodintril 163 1,3-bis (aminomethyl) cyclohexane <0 o-Phthalodintril 140 1,2-bis (aminomethyl) cyclohexane <0 p-Phthalodintril 224 1,4-bis (aminomethyl) cyclohexane <0

Example 4: Hydrogenation of optionally substituted bisphenols to cycloaliphatic diols

R1 Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C CH ₃ Bisphenol A 158 2,2-bis (4-hydroxycyclohexyl) -propane <50 H Bisphenol-F 162 Bis- (4-hydroxycyclohexyl) methane <50

Example 5: Hydrogenation of acid anhydrides and aromatic acids to the corresponding cycloaliphatic compounds

Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C phthalic anhydride 131 Cyclohexane-1,2-dicarboxylic anhydride 32 benzoic acid 121 cyclohexanecarboxylic 28

Example 6: Esterification of benzoic acid with various alcohols to the corresponding esters of benzoic acid

Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C benzoic acid 121 benzoate -12 121 benzoate -34 121 butyl benzoate -20

Example 7: Esterification of dicarboxylic acids with various alcohols to the corresponding esters of adipic acid

Feedstock (liquid to be pumped) Melting point ° C Reaction product "auxiliary liquid" Melting point ° C Adipic acid (n = 4) 151 dimethyl 10 151 diethyl -20 151 dibutyl -25 Glutaric acid (n = 3) 98 dimethyl -40 98 diethyl -24 Succinic acid (n = 2) 184 dimethyl 19 184 diethyl succinate -21

Example 8: Preparation of polyesters from dicarboxylic acids and diols

Feedstock * Melting point ° C "Auxiliary liquid" = diol Melting point ° C Adipic acid (n = 4) 151 ethylene glycol -16 Glutaric acid (n = 3) 98 diethylene glycol -6 Succinic acid (n = 2) 184 1,4-butanediol 20 phthalic anhydride 131 1,3-propanediol -26 terephthalic acid Sublimation at> 300 ° C ethylene glycol -16 * As a feedstock, for example, a melt of the feedstock, a concentrated solution of the feedstock or suspended finely divided solids of the feedstock ("slurry driving style") can be used with one of the auxiliary liquids mentioned in the right column or a process solvent.

Claims (12)

1. A method of continuously conveying a liquid (1) by means of a displacement pump (12) having physically separate forward-transport valves (10) and (11) and a liquid-filled bidirectional flow line (7) between displacement pump (12) and forward-transport valves, where an auxiliary liquid (3) whose melting point is below the melting point or below the saturation temperature of the liquid (1) to be conveyed is present in the bidirectional flow line (7), wherein the liquid (1) to be conveyed is used as starting material in a chemical reaction and the auxiliary liquid (3) is a product or a starting material of the chemical reaction.
2. The method according to claim 1, wherein the liquid is an organic compound.
3. The method according to claim 2, wherein the organic compound is an aromatic compound, the chemical reaction is a hydrogenation and the product of the hydrogenation of the aromatic compound is used as auxiliary liquid.
4. The method according to claim 3, wherein the aromatic compound is an aromatic amine.
5. The method according to claim 2, wherein the organic compound is a carboxylic acid or a carboxylic acid derivative, the chemical reaction is a process for preparing esters and the ester formed in the reaction or the alcohol used as starting material is used as auxiliary liquid.
6. The method according to at least one of claims 1 to 5, wherein the liquid has a melting point or a saturation temperature of from 50 to 300°C.
7. The method according to at least one of claims 1 to 6, wherein the melting point of the auxiliary liquid is 50°C or less.
8. The method according to at least one of claims 1 to 7, wherein the displacement pump is a diaphragm pump.
9. The method according to at least one of claims 1 to 8, wherein the auxiliary liquid is introduced continuously into the bidirectional flow line.
10. The method according to at least one of claims 1 to 9, wherein the ratio of the volume flow of auxiliary liquid to the volume flow of the liquid to be conveyed is in the range from 1:10 to 1:100.
11. The method according to at least one of claims 1 to 10, wherein the auxiliary liquid is introduced using a diaphragm pump.
12. The method according to at least one of claims 1 to 11, wherein the drives of the pump for conveying the auxiliary liquid and of the displacement pump are mechanically or electronically coupled to one another.

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