DE102006038476B4 - Continuous autoclave - Google Patents

Abstract

Apparatus for the continuous hydrothermal treatment of feed material, the apparatus being at least
a) a reaction section receiving the feedstock;
b) a heating device;
c) a device for generating pressure; and
d) comprises a product discharge section with a cooling device, which is connected downstream of a product outlet opening,
wherein the reaction section receiving the feed comprises at least one stirring element and at least one flow resistance element.

Description

The The present invention relates to a device for continuous hydrothermal treatment of substances. The device is for different Applications such as hydrothermal crystallization reactions suitable. Furthermore, the present invention relates to a corresponding Process for continuous hydrothermal treatment. Furthermore The present invention relates to the use of the device according to the invention or the method according to the invention for the production of crystalline or semi-crystalline nanoparticles and a specific method for producing nanoparticles or corresponding agglomerates.

The implementation or treatment of various materials under high temperature and high pressure conditions in an autoclave is a common method in various chemical fields. Thus, autoclaves are not only used for hydrogenations, saponifications, polymerizations, vulcanizations or organic syntheses, but also, for example, for crystallization processes or others single-phase transformations. Organic syntheses are another field of application for autoclaving processes. The hydrothermal crystallization is also used for the production of nanoparticles, for example ZrO ₂ nanoparticles. By way of example, reference is made to the publications "Hydrothermal synthesis of ceramic nanomaterials for functional applications" by Roxana M. Piticescu, RR Piticescu, D. Taloi and V. Badilita in Nanotechnology 2003, 14, pp. 312-317; "Hydrothermal synthesis of zirconia nanomaterials" by RR Piticescu, C. Monty, D. Taloi, A. Motoc and S. Axinte, published in J. Eur. Ceram. Soc. 2001, Vol. 21, no. 10-11, pp. 2057-2060 and "On the direct synthesis of noble metal cluster containing MCM-41 using surfactant stabilized metal nanoparticles" by JPM Niederer, ABJ Arnold, WF Hölderich, B. Spliethoff , B. Tesche, M. Reetz and H. Bönnemann in Stud. Surf. Sci. Catal. 2001, 135, p. 4780-4787.

Basically must between so-called batch autoclave and continuous Autoclaves are distinguished. For continuously working Autoclaves are pressure vessels used during the Production or implementation phase continuous educt or feed supplied and simultaneously discharged product will, while the operating temperature and the for the reaction necessary pressure in the autoclave are maintained.

By contrast, batch autoclaves are operated batchwise, ie discontinuously, ie the educts are fed to the autoclave, the autoclave is heated to the required operating temperature and the corresponding operating pressure is built up and after completion of the hydrothermal treatment to be carried out, the autoclave is cooled again and the product is removed. The batch mode of operation is associated with a correspondingly high expenditure of time and energy. The additional expenditure of time also results, in particular, from the fact that in hydrothermal syntheses the desired conversion proceeds only at an acceptable rate near the process temperature. This applies both to crystallization processes and to chemical syntheses and can be illustrated by the example of the synthesis of nanoparticulate ZrO ₂ : in the temperature range between room temperature and 150 ° C., no significant conversion from the amorphous precursor (eg. Zirconium (IV) hydroxide) is observed in the crystalline nanoparticulate product. At temperatures between 150 ° C and 200 ° C, the reaction starts slowly, but only above about 200 ° C to a significant increase in the reaction rate. When a process temperature of 230 ° C is reached, a minimum holding time of about 1 minute is enough to complete the reaction.

by virtue of the fact that the further the rate of turnover is the lower Reactor temperature is removed from the process temperature finds only a small part of the total batch process resulting heating time, the desired reaction or implementation. For autoclaving processes in batch mode not only does the heating phase take a considerable amount of time, but also the cooling phase before taking the product is of appropriate duration. from that results in a significant with the discontinuous operation connected time expenditure.

Of Further, the batch mode of operation requires one over the other continuous operation significantly higher energy consumption. The higher energy consumption is due in particular to the high heating phase. During the heating phase must the reactor or autoclave with a correspondingly high heating rate be brought to process temperature. After reaching the process temperature decreases the heat output to be applied and thus the energy consumption dependent on from the goodness of thermal insulation of the autoclave jacket significantly.

Furthermore Subject to operate in the batch mode of operation autoclave one experience significantly higher Material stress. This results from the constant heating and cooling and but concerns the heating element or the heater but also the Pressure vessel, in which the corresponding implementation is carried out.

Finally required a batch-mode hydrothermal reaction for understandable reasons also a significantly higher Personnel expenses.

Out the above reasons has a continuous autoclave opposite a batch autoclave significant benefits in terms of energy, time and personnel costs. However, these are usual in the prior art described continuously operating autoclave with regard to efficient litigation also with disadvantages connected. While in a discontinuously operated autoclave a complete reaction to the desired Ensure product without major difficulties lets (by leave the starting material to be treated in the autoclave for a sufficient time leaves), This is because of a continuous device of the permanent Inflow and outflow of educt and product not readily possible. Around a complete or predetermined implementation in a continuous autoclave To reach, the starting material or feed must be sufficiently long or over a predetermined duration of the required reaction temperature and be exposed to the necessary reaction pressure. Accordingly possess continuously working autoclave often a tubular or elongated Reaction chamber. The reaction of the feedstock or starting material takes place while of flowing through of the autoclave or during passing through the tubular Reaction zone.

The continuous reaction is characterized in that the load is continuously in fed to the reactor and the reaction products are constantly removed. For the Time, the substances or particles or fluid elements in a continuous operated reactor remain, the term "residence time" is used. The reactor flowing through Fluid particles are subject to varying degrees of mixing effects, for example, by stirring, Diffusion or hydrodynamic flow are caused. So are the residence times of particles that are simultaneously in one Reactor were fed, in reality, over a more or less wide Spectrum distributed. As in usual continuously operating tubular reactors, for example by turbulent Velocity variations or by vortex formations, mixing processes in axial Direction (flow direction) be caused, the residence time of the fluid particles is strong differently. As a result, a large part the educts are not or only insufficiently hydrothermally treated or implemented is because of the conversion and the yield of a chemical reaction below other of the reaction rate and the reaction time depend. Depending on the type of implementation or reaction may also be too long Residence time adversely affect (for example, because of Education unwanted By-products).

The previous versions show that the reaction in continuous autoclave of numerous factors is influenced and in particular the mixing effects one in the With regard to product specificity and sales oppose acceptable earnings.

Special Difficulties arise in addition when, as in crystallization reactions, suspensions in the be fed continuously working autoclave. From the above establish In principle, it offers a relatively long tube reactor with a relatively small diameter for the continuous hydrothermal Treatment to use, since the long flow time usually a ensures a sufficiently long reaction time. Residence times of several hours are in such, relatively slowly flowed through tubular reactors therefore not uncommon. However, such tubular reactors are suitable with a length of several meters and a diameter of only a few millimeters or only a few centimeters for crystallization processes of solid particles in a liquid medium. Made comprehensible establish it comes easily to the solid particles caused by deposits and blockages. A continuous operation of such a plant is therefore due to a high susceptibility to interference characterized. A particularly prone to failure area of such a continuous autoclave is the product outlet area or nozzle area. Usually the product is over a corresponding opening pumped out of the continuous reactor, the material flow in the area of the opening is throttled. In the nozzle area Therefore, it always exists in the passage of solids containing material the danger of deposits and constipation. The nozzle of a Consequently, continuous autoclave is of diameter not arbitrarily small interpretable. In this context is simultaneous to note that the smallest possible Nozzle too the maximum possible residence time and defines the maximum achievable pressure / temperature level in the reactor.

in view of Of the disadvantages mentioned above, it would be desirable to have a device and a method for continuous hydrothermal treatment to have feed or starting materials available, which in particular also for crystallization syntheses are suitable and which avoid the above-mentioned disadvantages.

An object of the present invention is therefore to provide a continuously operating device for the hydrothermal treatment of feed and a entspre ing process, which reduces the unwanted axial mixing effects described, ensures a radial mixing and at the same time avoids excessively long dwell times, for example of several hours. Moreover, it was an object of the present invention to provide a continuous apparatus for the hydrothermal treatment of feed material, in which also solids-containing feed can be implemented or treated and at the same time reduces or avoids unwanted solid deposits. It is a particular object of the present invention to provide a device and a corresponding method which permits particle syntheses and in particular the production of nanoparticles from corresponding precursors in a continuous hydrothermal reaction.

above Tasks are performed by the inventive device for continuous hydrothermal treatment of feed, the inventive method for the hydrothermal treatment of feed material and the method according to the invention for the preparation of a suspension of crystalline, semi-crystalline and / or compacted nanoparticles dissolved.

In the following section, some terms used in the present application are explained in more detail:
For the purposes of the present invention, a "hydrothermal treatment" is a treatment of an aqueous or nonaqueous solution or suspension under elevated pressure and elevated temperature (for example at a temperature above the boiling point of the solvent or suspension medium) leading to a chemical or material transformation or modification of the feedstock or educt leads.
When the term "residence time" is used in the present invention, it means the mean residence time τ. The mean residence time τ can be determined experimentally via the residence time distribution by standard methods or via the total volume of the reactor and the throughput (total volume of reactor / volume per minute = τ).
"Nanoparticles" in the sense of the present invention are particles having an average particle diameter (also referred to as average particle size) of not more than 100 nm or else re-dispersible agglomerates of such particles. Unless stated otherwise, the average particle diameter is taken to mean the particle diameter in relation to the volume average (D ₉₀ value). The D ₉₀ value is determined by means of dynamic light scattering, for example with an UPA (Ultrafine Particle Analyzer). The principle of dynamic light scattering is also known by the terms "photon correlation spectroscopy" (PCS) or "quasi-elastic light scattering" (QELS). For particularly small particles, quantitative electron microscopic methods (in particular TEM) can also be used. In addition, X-ray diffraction (XRD) can also be used to determine primary particle size.
The term "feed material" in the sense of the present invention comprises the educts to be treated, which are optionally suspended in a medium, for example in a water-based medium or nonaqueous medium. The feed material can also be a single-phase liquid containing the educts.
"Crystalline particles" in the sense of the present invention essentially consist entirely of crystalline phase, ie essentially no amorphous portion or no measurable amorphous portion is present.
According to the present invention, "dense particles" are particles which are for the most part or substantially densified to a maximum extent, that is to say they are not further compressible with respect to their chemical structure. For example, less ordered regions occurring in the outer region of nanoparticles can be further densified by hydrothermal treatment.
"Partially crystalline particles" in the sense of the present invention are particles which contain both crystalline and amorphous fractions. The proportion of crystalline or amorphous phase can be determined, for example, by means of X-ray diffraction diagrams or X-ray structure analysis (XRD).

• a) einen das Beschickungsgut aufnehmenden Reaktionsabschnitt;
• b) eine Heizvorrichtung;
• c) eine Vorrichtung zur Druckerzeugung; und
• d) einen Produktaustragungsabschnitt mit einer Kühlvorrichtung, die einer Produktaustrittsöffnung nachgeschaltet ist, wobei der das Beschickungsgut aufnehmende Reaktionsabschnitt wenigstens ein Rührelement und wenigstens ein Strömungswiderstandselement aufweist.

The device according to the invention for the continuous hydrothermal treatment of feed material comprises at least

• a) a reaction section receiving the feedstock;
• b) a heating device;
• c) a device for generating pressure; and
• d) a Produktaustragungsabschnitt with a cooling device, which is connected downstream of a product outlet opening, wherein the feed material receiving the reaction section comprises at least one stirring element and at least one flow resistance element.

• a) kontinuierliche Zufuhr des Beschickungsgutes in den Reaktionsabschnitt;
• b) hydrothermale Behandlung des Beschickungsgutes im Reaktionsabschnitt; und
• c) kontinuierlicher Austrag des hydrothermal behandelten Beschickungsguts durch die Produktaustrittsöffnung in den Produktaustragungsabschnitt,

wobei das Produkt im Produktaustragungsabschnitt auf Normaldruck gebracht und mit Hilfe einer Kühlvorrichtung abgekühlt wird.Furthermore, the invention relates to a method for the hydrothermal treatment of feed material in a device having a feed section receiving the feedstock and a product discharge section downstream of a product discharge opening, the method comprising the following steps:

• a) continuous feed of the feedstock in the reaction section;
• b) hydrothermal treatment of the charge in the reaction section; and
• c) continuous discharge of the hydrothermally treated feed through the product outlet into the product discharge section,

wherein the product is brought to normal pressure in the product discharge section and cooled by means of a cooling device.

• a) kontinuierliche Zufuhr einer Suspension amorpher und/oder teilkristalliner Partikel in einem Medium in den Reaktionsabschnitt;
• b) Kristallisation und/oder Verdichtung der amorphen und/oder teilkristallinen Partikel mittels hydrothermaler Behandlung im Reaktionsabschnitt; und
• c) kontinuierlicher Austrag der kristallinen, teilkristallinen und/oder verdichteten Nanopartikel und/oder Agglomerate durch die Produktaustrittsöffnung in den Produktaustragungsabschnitt,

wobei das Nanopartikel-haltige Medium im Produktaustragungsabschnitt auf Normaldruck gebracht und mit Hilfe einer Kühlvorrichtung abgekühlt wird.Furthermore, the present invention relates to an apparatus and a method for producing a suspension of crystalline, partially crystalline and / or compacted nanoparticles or corresponding re-dispersible agglomerates of nanoparticles. The inventive method for producing a suspension of crystalline, partially crystalline and / or compressed nanoparticles in a device having a reaction section and a product discharge section, which is connected downstream of a product outlet opening, comprises the following steps:

• a) continuous supply of a suspension of amorphous and / or partially crystalline particles in a medium in the reaction section;
• b) crystallization and / or densification of the amorphous and / or semicrystalline particles by means of hydrothermal treatment in the reaction section; and
• c) continuous discharge of the crystalline, partially crystalline and / or compacted nanoparticles and / or agglomerates through the product discharge opening into the product discharge section,

wherein the nanoparticle-containing medium is brought to normal pressure in the product discharge section and cooled by means of a cooling device.

According to the present Invention was surprisingly found that it is possible with the aid of the device according to the invention undesirable to reduce axial mixing and at the same time the desired mixing ensure or generate in the radial direction. This succeeds in particular by the attachment of one or more flow resistance elements and one or more stirring elements inside the reaction section. The aforementioned reaction section is the reactor space in which the hydrothermal treatment takes place. As the device of the invention is operated continuously, the reaction section at least an inflow opening and at least one product outlet opening or nozzle. According to one advantageous embodiment the reaction section has a substantially cylindrical shape on, preferably with a length from 1500 mm to 4000 mm, particularly preferably with a length of 1600 mm to 2000 mm and / or an inner diameter of 50 to 250 mm, preferably with an inner diameter of 100 to 150 mm.

In principle, stirring favors the necessary vertical or radial medium mixing, but also the axial mixing, which is undesirable because freshly pumped material spreads too quickly throughout the reactor and a large proportion of unreacted starting material leaves the autoclave. In the case of nanoparticle syntheses such as, for example, the ZrO ₂ synthesis, this leads, in addition to a too low product crystallinity, to an increase in the product viscosity. As a result, the flow is continuously reduced and the risk of nozzle clogging is significantly increased.

Around undesirable To reduce or avoid axial mixing, according to the present Invention at appropriate intervals one or more flow resistance elements inside the reaction section, preferably at one of the autoclave or reaction section passing stirrer shaft attached. The flow resistance elements are designed according to the invention that they are unwanted Mixing effects, especially mixing effects in axial Direction or flow direction counteract. It has been found that by the flow resistance elements according to the invention the unwanted mixture can be significantly reduced in the axial direction.

According to one particularly preferred embodiment this is at least one flow resistance element designed like a disk, wherein the surface normal parallel to the longitudinal axis the device is. In a particularly preferred embodiment contains the device according to the invention at least two, more preferably at least three, and most preferably at least four flow resistance elements, which are preferably designed disk-like and particularly preferred at one along the longitudinal axis the device running agitator shaft are attached. The distances between the flow resistance elements depend among other things on the flow velocity with the the reaction section is flowed through by the medium or the middle Dwell time. It was found that at a flow rate from 0.5 to 0.8 l / min and a mean residence time in the range from 16 to 26 minutes, a distance of 50 mm and 150 mm between the flow resistance elements is advantageous. It has furthermore been found that in the case of low-viscosity autoclaving media with more tendency to flow resistance elements better separation effects can be achieved or an axial mixing is better reduced.

According to a particularly preferred embodiment, the disk-like flow resistance elements have one or more vent holes or vent holes, preferably with a diameter of 3 to 10 mm and most preferably with a diameter of about 5 mm, on. The aforementioned "holes" prevent the accumulation of gas bubbles generated in the liquid medium during the autoclaving process on the flow resistance elements or substantially reduce this undesirable accumulation of gas bubbles. According to a further advantageous embodiment, the distance between the disk-like designed flow resistance elements and the reactor wall is less than 10 mm, preferably less than 5 mm and particularly preferably about 1 mm.

The at least one stirring element according to the invention is designed so that a sufficient or complete mixing is ensured in the radial direction. According to the present invention be at appropriate intervals one or more stirring elements inside the reaction section, preferably at one of the autoclave or Reaction section passing stirrer shaft attached. In a particularly preferred embodiment contains the device according to the invention at least two, more preferably at least five, and most preferably at least ten stirring elements. Particularly preferred according to the present Invention propeller stirrer, preferably 4-winged propeller used as stirring elements. Alternatively or in addition can 2-, 3- or multi-leaved propeller, Blade stirrer or anchor are used, preferably at one along the longitudinal axis the device running agitator shaft are attached.

According to a particularly preferred embodiment, the at least one flow resistance element is arranged such that it divides the reaction section into a plurality of segments along the flow direction, wherein the segments preferably have a length in the range between 50 and 1000 mm. A schematic representation of a device according to the invention is shown in FIG 1 shown.

According to one another preferred embodiment, the heater extends substantially over the whole length the reaction section and preferably along the reaction section at least 2, preferably at least 3 independently temperature-controlled Heating zones on. The heating zones can For example, by means of so-called winding heating, which on the den Reaction section surrounding reactor shell are arranged independently be heated. In this way, the temperature control can be along of the reaction section over different Control tempered heating zones. The winding heaters preferably enclose almost complete the reactor jacket and can heat the autoclaving medium very rapidly while in the reactor, preferably a narrow or oblong Design has fallen down. The embodiment of the invention the device allows the implementation of hydrothermal reactions with compared to conventional Autoclave significantly shorter Residence times, as through the installation of flow resistance elements and stirrers a relatively wider Reaction section (large diameter in cylindrical design) can be realized and a rapid warming the flowing through Medium possible is.

According to one further advantageous embodiment becomes the temperature guide monitored by several thermocouples and regulated by the measured temperatures. Preferably measures at least one thermocouple each the temperature of the feed in the reaction section immediately before the product outlet opening and in the entry region of the reaction section and preferably measure at least two thermocouples the temperature at different points the reactor jacket surrounding the reaction section. The medium thermocouples serve the immediate control of the reaction conditions.

According to one Another aspect of the present invention, a product outlet opening or Nozzle provided, the hydrothermal treatment of suspensions or the execution allowed by particle syntheses. The product outlet opening according to the invention the reaction section, which is also referred to as a nozzle below is, is preferably with respect their geometry designed so that a deposit of solid particles in the area of the product outlet is essentially prevented. The product outlet opening according to the invention can with a nozzle be provided, wherein the product outlet opening of the device according to the invention designed like a nozzle can be or the nozzle as a separate part attached to or in the product outlet opening can be.

It has proved to be particularly advantageous in the flow direction to use conically widening designed nozzle. The product outlet has according to a particularly preferred embodiment a cone-shaped Form, wherein the cone is arranged so that its tip against the flow direction into the interior of the reaction section shows and the product passage from the reaction section to the product discharge section an opening done in the top of the cone.

The shape of the product outlet or nozzle is of particular importance in particle syntheses. If, for example, a "classic" hollow cone shape is used, with the tip pointing in the direction of flow, the slope of the in neren wall of the hollow cone within a short time material from. This is then pressed by the liquid flow in the cylindrical portion of the actual opening and clogged the nozzle. A substantial increase in the diameter of the product outlet opening would possibly avoid blockages, but would discharge so much material that neither the required temperature nor the required residence time for example, a nanoparticle synthesis is achieved. In a cone which is aligned with the tip in the direction of flow and serves as the nozzle according to the invention, the nozzle tip or nozzle bore acts as a tear-off edge on which no or little material can be deposited. A schematic representation of a preferred embodiment of the nozzle according to the invention is shown in FIG 2 shown.

The nozzle according to the invention preferably consists of hard stainless material, more preferably of CrNiMo steel (1.4435) with a hard metal tip. The nozzle preferably has an overall length in the range of 50 mm to 150 mm, more preferably between 80 and 100 mm. The length of the preferably cylindrical passage opening Z (see 2 ) is preferably between 1 to 5 mm and more preferably 3 mm. In a further preferred embodiment, the product outlet opening or nozzle can be coated with a material which counteracts the deposition of particles. The product outlet orifice preferably has a substantially circular opening with a diameter in the range of 0.2 to 1.5 mm, more preferably 0.4 to 1 mm, and particularly preferably 0.6 to 0.8 mm. In the hydrothermal treatment of dissolved educts even significantly smaller openings can be used.

According to one further advantageous embodiment contains the inventive device a Level sensor to regulate inflow and outflow. The Feickgutgut- or Eduktzuführung via a High pressure pump which the medium as a suspension or solution in the Reaction section of the autoclave continuously fed. The Pumping power is determined by the pressure prevailing in the reaction section and the flow rate through the product outlet (nozzle) determined. To control the pump power, the level in the reactor room can constantly with Help of a level probe be measured. The level probe is transmitted electrical signals to a control unit which the pump power according to the level lowered or raised (with decreasing level the pump power is increased, at rising level decreased). According to a preferred embodiment is a high-temperature stable, preferably Teflon-coated or zirconia-walled resistive probe or high pressure rod probe used.

• a) kontinuierliche Zufuhr des Beschickungsgutes in den Reaktionsabschnitt;
• b) hydrothermale Behandlung des Beschickungsgutes im Reaktionsabschnitt; und
• c) kontinuierlicher Austrag des hydrothermal behandelten Beschickungsguts durch die Produktaustrittsöffnung in den Produktaustragungsabschnitt. Das Produkt bzw. das Produkt-haltige Medium wird erfindungsgemäß im Produktaustragungsabschnitt auf Normaldruck gebracht und mit Hilfe einer Kühlvorrichtung abgekühlt. Die Abkühlung des Produkts im Produktaustragungsabschnitt erfolgt gemäß einer bevorzugten Ausführungsform, indem der Produktstrom durch ein Rohr geführt wird, welches über einen das Rohr umgebenden kühlmittelhaltigem Kühlmantel gekühlt wird, wobei die Kühlmitteltemperatur vorzugsweise im Bereich zwischen 5 und 15°C liegt.

Another object of the present invention relates to a method for the hydrothermal treatment of feed material in a device with a receiving portion receiving the feed and a product discharge section, which is connected downstream of a product outlet opening. The method according to the invention comprises at least the following steps:

• a) continuous feed of the feedstock in the reaction section;
• b) hydrothermal treatment of the charge in the reaction section; and
• c) continuous discharge of the hydrothermally treated feed through the product discharge opening into the product discharge section. According to the invention, the product or the product-containing medium is brought to normal pressure in the product discharge section and cooled with the aid of a cooling device. The cooling of the product in the Produktaustragungsabschnitt is carried out according to a preferred embodiment by the product stream is passed through a tube which is cooled by a surrounding the tube coolant cooling jacket, wherein the coolant temperature is preferably in the range between 5 and 15 ° C.

According to one advantageous embodiment of the method according to the invention is carried out Feed the feed into the reaction section using a high-pressure pump, which is capable of the load against a pressure in the range of 20 to 100 bar and against a temperature from 100 to 300 ° C pump into the reaction section. Typical pressure and temperature ranges are at 40 to 60 bar and 230 to 250 ° C.

It is preferred, the continuous feed into the reaction section and the continuous discharge from the reaction section with Monitoring the help of a level probe and over a corresponding control unit connected to the probe regulate. According to one preferred embodiment be with the inventive method Residence times of not more than 60 minutes, preferably not more achieved as 30 min and more preferably of not more than 20 min. The degree of conversion in a crystallization reaction (corresponds the crystalline fraction in the product) is typically between 70 and 90% and preferably over 75%.

The heating of the feed material in the reaction section preferably takes place via the heating of the reactor jacket surrounding the reaction section. The medium is fed according to an advantageous embodiment, cold (room temperature) or preheated in the reactor and heated to the reaction temperature via the heated reactor wall when flowing through the reaction section. Preferably, the feed is pressed from above by means of a high pressure pump in the reaction section. The heating may take place in at least two, preferably at least three, heating zones arranged around the reactor jacket, wherein the heating zones may have different temperatures.

The hydrothermal treatment of the feed in the reaction section preferably with stirring with stirring speeds in the range of 50 to 200 rpm. The mean residence time of the too treated feed in the reaction section is preferably a maximum of 3600 s, more preferably a maximum of 1800 s and especially a maximum 1500 s. The mean residence time is mainly built up by the Pressure (which is directly related to the medium temperature), the length of the Reaction section and the diameter of the product outlet opening or Nozzle determined. The for the respective hydrothermal conversion optimum result can be determine by appropriate test series.

The Practical operation or control of the system can be done via a Control unit or via a user software installed on a separate computer. The actual control software of the device is preferably installed in the control unit.

According to one Another aspect of the present invention is the inventive method for the hydrothermal treatment in the device according to the invention described above.

One suitable field of application for the inventive method and the device according to the invention but is also in the range of single-phase transformations (liquid A → liquid B) such as organic syntheses. In particular in relation on the reaction rate slowly running hydrothermal Reactions can be according to the present Perform invention, since in a pure fluid system the product discharge opening or nozzle chosen very small can be and thus longer Residence times in the reactor can be achieved. Also implementations that require a fumigation, such. B. let catalytic hydrogenations with the device according to the invention or implement the method. The fumigation takes place in such Reactions preferably from above (gas feed connection in the reactor cover), or by means of gassing stirrers, which preferably penetrate the entire medium volume.

in principle can all particle syntheses that can be realized in a batch reactor are, also on a continuous way in the device according to the invention or produced by the method according to the invention become.

• a) kontinuierliche Zufuhr einer Suspension amorpher und/oder teilkristalliner Partikel in einem Medium in den Reaktionsabschnitt;
• b) Kristallisation und/oder Verdichtung der amorphen und/oder teilkristallinen Partikel mittels hydrothermaler Behandlung im Reaktionsabschnitt; und
• c) kontinuierlicher Austrag der kristallinen, teilkristallinen und/oder verdichteten Nanopartikel durch die Produktaustrittsöffnung in den Produktaustragungsabschnitt, wobei das Nanopartikel-haltige Medium im Produktaustragungsabschnitt auf Normaldruck gebracht und mit Hilfe einer Kühlvorrichtung abgekühlt wird.

The invention further relates to a process for producing a suspension of crystalline, partially crystalline and / or compacted nanoparticles and / or agglomerates of the abovementioned particles, the process comprising at least the following steps:

• a) continuous supply of a suspension of amorphous and / or partially crystalline particles in a medium in the reaction section;
• b) crystallization and / or densification of the amorphous and / or semicrystalline particles by means of hydrothermal treatment in the reaction section; and
• c) continuous discharge of the crystalline, partially crystalline and / or compacted nanoparticles through the product outlet opening into the product discharge section, wherein the nanoparticle-containing medium is brought to normal pressure in the product discharge section and cooled by means of a cooling device.

The above in connection with the device according to the invention for hydrothermal Treatment of feed and the method according to the invention described for the hydrothermal treatment of feed Embodiments, are also in combination in a corresponding manner to the inventive method for the preparation of a suspension of crystalline, semi-crystalline and / or compacted nanoparticles or agglomerates of nanoparticles applicable.

The Preparation of the educt particles can be carried out in the usual manner, for. B. by gas-phase condensation processes, sol-gel processes, precipitation processes, Colloid techniques, plasma processes, flame pyrolysis, MOCVD processes, etc. The aforementioned methods are described in detail in the literature. Particularly preferred according to the present Invention prepared by sol-gel method or precipitation method Particles used. In the suspensions used according to the invention is it in a liquid Medium suspended solid particles or solid particles from each any suitable material. Preference is given to inorganic particles and particularly preferably used particles of metal compounds.

Particularly preferred materials for the process according to the invention are oxide particles or hydrated oxide particles, in particular metal or semimetal oxides, hydrated metal or semimetal oxides or mixtures thereof. Especially before oxides or hydrated oxides of Mg, Ca, Sr, Ba, Al, Si, Sn, Sb, Pb, Bi, Ti, Zr, V, Mn, Nb, Ta, Cr, Mo, W, Fe, Co, Ru , Zn, Ce, Y, Sc, Eu, In, and La or mixtures thereof. Particularly preferred examples are ZrO ₂ , TiO ₂ , SnO ₂ , In ₂ O ₃ , Al ₂ O ₃ , indium tin oxide (ITO) and antimony tin oxide (ATO).

With the process according to the invention, it is possible to prepare crystalline, partially crystalline or compacted inorganic nanoparticles from the abovementioned, preferably amorphous or semicrystalline starting materials or precursors, such as, for example, nanoparticles of Al ₂ O ₃ , AlO (OH), ZrO ₂ , TiO ₂ , SiO ₂ , Fe ₃ O ₄ and SnO ₂ and mixtures thereof.

Obtained according to the invention Agglomerates of nanoparticles can be, for example, by mechanical Treatment (eg in a ball mill) of a suspension of the agglomerates in a dispersing medium, in particular carboxylic acids or Oxoxcarbonsäuren re-disperse. For example, you can 3,6,9-trioxadecanoic or acetic acid be used as a dispersing medium.

EXAMPLE

In the device according to the invention were according to the method of the invention starting from an amorphous precursor crystalline or partially crystalline Zirconia nanoparticles produced.

a) Preparation of the amorphous precursor

To 3800 g of a 70% solution of zirconium (IV) propylate in isopropanol (commercial product from Lehmann & Voss) is added with stirring a 4-fold molar excess of water (585 g). The precipitation reaction produces 1293 g of zirconium (IV) hydroxide, Zr (OH) ₄ and 1949 g of propanol. The precipitation is almost complete. The resulting aqueous solution contains the Zr (OH) ₄ in a concentration of 18% by weight. The aqueous zirconium hydroxide solution obtained is subjected in the second process step to a hydrothermal treatment according to the invention in the continuous reactor according to the invention.

b) Treatment of the amorphous precursor in continuously working autoclave

The according to step a) obtained amorphous precursor is in an autoclave according to the invention in crystalline nanoparticulate Zirconium oxide particles or corresponding re-dispersible agglomerates converted.

contraption

The Beschickungsgut- or Eduktzuführung carried out using a High pressure pump which the aqueous solution of zirconium hydroxide in the reaction space of the autoclave from above fed continuously. The pumping power is through the in the reactor prevailing pressure and the outflow velocity through the product outlet opening (nozzle) determined. To control the pump power, the level in the reactor room is constantly with Help of a level probe measured. The level probe is transmitted electrical signals to a control unit which the pump power according to the level lowered or raised (when the level drops increases pumping power, with increasing filling level decreased). As a level probe is a high temperature stable Teflon-coated or zirconium oxide-walled Resistance probe used.

The actual reaction section, ie the autoclave has a length of 1600 mm and an inner diameter of 110 mm. The reactor is made of stainless steel (1.4435, CrNiMo steel). The shaft arranged lengthwise inside the reaction space also consists of 1.4435 steel. Along the shaft there are eight steel cutting discs at a distance of about 110 mm as flow resistance elements and eleven four-bladed propeller stirrers at a distance of about 110 mm (see 1 ). The disk-like flow resistance elements each have two opposite vent holes with a diameter of about 5 mm. The distance between the disk-like designed flow resistance elements and the reactor wall is in each case about 1 mm. The shaft with the discs and 4-bladed propeller stirrers is driven by a stirrer motor mounted on top of the apparatus at about 100 rpm.

Of the Reaction section is divided into three heating zones, which are independent of each other can be tempered or regulated. The reactor temperature comes with five thermocouples measured. One is on each heater, two others measure the Temperature above and below in the medium. The medium thermocouples serve the immediate control of the reaction conditions.

The Product outlet opening The apparatus used consists of a nozzle made of stainless CrNiMo steel (1.4435) is made with a hard metal tip. The in the flow direction conically widening configured nozzle (conical shape) has a total length of 91 mm and a diameter of 0.65 mm. After flow through the Reactor passes through the autoclaving initially a pneumatically controlled Valve before it by means of the outlet nozzle continuously from the autoclave is discharged.

The cooling device installed in the product discharge section is composed of a cooling jacket and a cooling pipe wound therein with a Ge total length of 495 mm and a diameter of 10 mm. The cooling jacket and the cooling tube are made of 1.4435 steel. The cooling jacket is cooled to 10 ° C via a coolant and an external cooling unit. This cools the temperature of the product to 35-60 ° C as it exits the cooler.

crystallization

at the implementation the hydrothermal treatment is the precursor obtained in step a) with Help the high-pressure pump fed continuously to the reaction zone. For the generation the zirconia nanoparticles, the jacket temperature is set to 320 ° C. The medium temperature (measured indirectly before the product outlet opening) is about 240 ° C. The resulting from the medium temperature reaction pressure is approximately in the range of 45 bar. After the hot medium passes the outlet nozzle has, by the pressure of the flowing mass directly into one Condenser (cooling device) pushed, in which to about 40 ° C. chilled becomes.

The average residence time was determined by labeling (dye addition) or Auslitern determined. This is in the operating state of the reactor about 20 minutes and results from a total volume of the reactor of about 13 liters and a flow rate of 0.65 l / min.

The hydrothermal treatment of precursor a) in the continuous autoclave results in the formation of zirconia having the following composition:
75-85% crystalline phase, of which 25-35% monoclinic and 65-75% tetragonal; and
15-25% amorphous fraction. The crystalline portion and the amorphous portion were determined by X-ray diffraction analysis (XRD).

The Particle size of the as re-dispersible agglomerate nanoparticles is in the range between 20 to 30 nm. The resulting agglomerate of nanoparticles has a particle size between 200 and 300 nm. The particle size or the particle diameter was determined by dynamic light scattering determined with the help of a UPA of the company Grimm.

Claims (27)

Apparatus for continuous hydrothermal Treatment of feed, the device at least a) a reaction section receiving the charge; b) a heater; c) a device for generating pressure; and d) a product discharge section with a cooling device, that of a product outlet downstream, comprises, where the the feed receiving reaction section at least one stirring element and at least one Flow resistance element having. Device according to claim 1, characterized in that the heater substantially over the whole length of the reaction section. Device according to claim 2, characterized in that that the heating device along the reaction section at least 2, preferably 3 independently has heating zones that can be temperature-controlled by one another. Device according to one of the preceding claims, characterized in that the heating device is outside the area surrounding the reaction section Reactor shell is arranged and preferably wound heating elements having. Device according to one of the preceding claims in that the product outlet opening is provided with a nozzle is. Device according to claim 5, characterized in that that the geometry of the nozzle is designed so that a deposit of solid particles in the Area of the product outlet is essentially prevented. Device according to one of claims 5 or 6, characterized that the nozzle in the flow direction is conically widening designed. Device according to one of the preceding claims characterized in that the product outlet opening is a substantially circular opening with a diameter in the range of 0.2 to 1.5 mm, more preferably from 0.4 to 1 mm, and more preferably from 0.6 to 0.8 mm. Device according to one of the preceding claims in that the at least one stirring element and / or the at least one Flow resistance element at one along the longitudinal axis the device running agitator shaft is attached / are. Device according to one of the preceding claims characterized in that the at least one stirring element is a propeller stirrer. Device according to one of the preceding claims, characterized in that the at least one flow resistance element from so is designed to counteract mixing in the axial direction. Device according to one of the preceding claims, characterized characterized in that the at least one flow resistance element disc-like is configured, the surface normal parallel to the longitudinal axis the device is. Device according to one of the preceding claims characterized in that the at least one flow resistance element so is arranged so that it is the reaction section along the flow direction divided into several segments, the segments preferably a length in the Range between 50 and 1000 mm. Device according to one of the preceding claims characterized in that the reaction section of the device substantially vertically, preferably flows through from top to bottom. Device according to one of the preceding claims in that the device comprises a level measuring probe for regulating Having inflow and outflow. Device according to one of the preceding claims characterized in that the reaction section is a substantially cylindrical shape, preferably with a length of 1500 mm to 4000 mm, more preferably with a length of 1600 mm to 2000 mm and / or an inner diameter of 50 to 250 mm, more preferably with an inner diameter of 100 to 150 mm Process for the hydrothermal treatment of feed material in a device with a charge receiving the Reaction section and a Produktaustragungsabschnitt, the one Product outlet opening downstream, the method comprising the following steps: a) continuous feeding of the feed into the reaction section; b) hydrothermal treatment of the charge in the reaction section; and c) continuous discharge of the hydrothermally treated Feed through the product outlet into the product discharge section, in which the product is brought to normal pressure in the product discharge section and with the help of a cooling device chilled becomes. Method according to the preceding claim 17, characterized characterized in that the feed of the feed into the reaction section with the aid of a device for generating pressure. Method according to one of the preceding claims 17 or 18 characterized in that the continuous supply and the continuous discharge monitored by means of a level probe and over regulates a corresponding control unit connected to the probe becomes. Method according to one of the preceding claims 17 to 19, characterized in that the heating of the feed in the reaction section over the warming the reactor jacket surrounding the reaction section takes place. Method according to one of the preceding claims 17 to 20, characterized in that the heating in at least two, preferably at least three arranged around the reactor jacket heating zones takes place, wherein the heating zones may have different temperatures. Method according to one of the preceding claims 17 to 21, characterized in that the hydrothermal treatment of the Charged material in the reaction section is carried out with stirring. Method according to one of the preceding claims 17 to 22, characterized in that the residence time of the treated Feed in the reaction section a maximum of 12 h, preferably not more than 3600 seconds, more preferably not more than 1800 seconds and more preferably maximum 1500 s. Method according to one of the preceding claims 17 to 23, characterized in that the cooling of the product in the product discharge section takes place by passing the product stream through a tube, which preferably over a coolant containing the tube Cooling jacket is cooled, where the coolant temperature preferably in the range between 5 and 15 ° C. Method according to one of the preceding claims 17 to 24, characterized in that the temperature control monitored by means of several thermocouples and optionally regulated, preferably at least each thermocouple the temperature of the feed in the reaction section immediately before the product outlet and in the upper part of the Reaction section measures and preferably at least two thermocouples the temperature at different points of the reaction section measure surrounding reactor jacket. Method according to one of the preceding claims characterized in that the method is used in a device according to the claims 1 to 16 performed becomes. Method according to one of the preceding claims, thereby characterized in that the method comprises the following steps: a) continuous supply of a suspension of amorphous and / or partially crystalline Particles in a medium in the reaction section; b) crystallization and / or densification of the amorphous and / or semi-crystalline particles by hydrothermal treatment in the reaction section; and c) continuous discharge of the crystalline, semi-crystalline and / or densified nanoparticles and / or corresponding agglomerates the product outlet in the product discharge section, where the nanoparticle-containing Medium in the product discharge section brought to normal pressure and with Help a cooler chilled becomes.