EP2237866B1

EP2237866B1 - Apparatus for producing titanate nanostructures

Info

Publication number: EP2237866B1
Application number: EP08865266A
Authority: EP
Inventors: Imre Kiricsi; Zoltán KÓNYA; Ákos KUKOVECZ; Endre HORVÁTH
Original assignee: University of Szeged
Current assignee: University of Szeged
Priority date: 2007-12-21
Filing date: 2008-12-20
Publication date: 2011-08-31
Anticipated expiration: 2028-12-20
Also published as: EP2237866A1; WO2009081218A1; HU0700228V0; ATE522270T1; HU3460U

Abstract

This invention relates to a device for producing titanate nanostructures from titanate containing material by way of an alkali-hydrothermal treatment, the device contains at least a vessel (1) to be closed by a closure cap (F) and said vessel (1) is rotatable around an axis (T), and a mixing device arranged inside the vessel (1), a heating device (H), and the centreline (k) of said axis (T) is a line penetrating the vessel (1), and said mixing device is at least one rod freely movable inside the vessel (1).

Description

This invention relates to a device for producing titanate nanostructures by means of alkali-hydrothermal process starting from titanium containing base material, the apparatus contains at least a vessel to be closed by a closure cap and said vessel is rotatable around an axis, and a mixing device arranged inside the vessel, and it is provided by a heating means.
Titanium dioxide is nowadays being in a prominent position among different titanium-oxide compounds, since its white colour and easy-to-produce feature in mass production allow its use in dyes and coverings as a pigment material.
It can be used as a white pigment filler material in polymers allowing a variation of transparency to the polymer, depending on its the particle size.
A further possibility to be exploited in dyestuff industry is the photocatalitic feature of the titanium-dioxide, that is electron-hole pairs are formed in its adequate sized crystals influenced by light, initiating chemical reactions. This feature of the titanium dioxide might be exploited if it is built into a matrix material providing an effect of delivering a material to be oxidized, i.e. a contaminant, from the gas phase onto the surface of the titanium-dioxide particle. To achieve this effect an aerated matrix material is needed, indeed. An essential demand for the titanium dioxide that the size of most of its particles be in a range of nanometre orders. The simplest successful solution is directly adhering titanium-oxide nanoparticles to the oxidizing surface. Such a solution may be the production of a self-cleaning glass surface.
An other group of titanium-oxide compounds is the family of trititanates. Nanosized, tubular structures can be synthesized from these materials. The practical use of these nanotubes is altogether not yet disclosed. It is recognised that they have no any photocatalitic feature. Also, there is no known result of research and development relating to its tubular structure. Since the titanate tubes have a helical form that is they are similar to a spirally wound plate, and contain ion exchange cations, its future practical use may have concern with these features.
Nanotubes made by hydrothermal method have an inner diameter between 4 and 6 nm, and an outer diameter between 9 and 11 nm. Their average length is between 100 and 130 nm.
Nanofibres made by hydrothermal method are formations without an inner channel and having an average diameter between 30 and 60 nm and diameter/length ratio between 1:10 - 1:10000.
Patent document JP 2006089307 discloses a synthesis method of long and cheap titanium-oxide nanotubes. During production of titanium-oxide nanotubes a bulk of granulate containing titanium and placed in a reaction chamber of a reaction vessel having no inner mixing members is treated hydrothermally, while the reaction vessel placed in a furnace is being rotated around a horizontal axis. This device has two reaction vessels mounted opposite each other in a common axis. In this arrangement the synthesis of the titanate nanostructure takes place at a temperature above 100 °C, and by a NaOH concentration above 5 mol. The disadvantage of this solution is that above 5 rpm the product obtained is set on the side of the reaction chamber opposite the axis as a hard, inhomogeneous layer. Another related prior art is disclosed in US 6484 568B1
Rotation of the reaction chamber is necessary to decrease the diffusion limit having a key role in kinetics of reaction, but at the same time, as mentioned above, the reaction products, due to the effect of the centrifugal force, form a sediment on a surface placed in the direction of the centrifugal force. The highest the rotational speed the lower the diffusion limit mentioned, but the highest the forming of sediments due to the increasing centrifugal force as well, and then the diffusion decreases again in a hard sediment. Up to the present this adverse effect has been failed to eliminate by means of devices according to the state of the art.
Therefore, the object of the present invention is to provide a device for producing titanate nanostructures using rotation necessary to decrease diffusion limit, but decreasing or eliminating sediment forming effect thereof, thus creating a simple and inexpensive apparatus suitable for producing nanofibres being longer and having a greater specific surface area than that of known nanostructures, and to make a product having loose and foamy consistency rather than a hard sediment, even by high number of revolution.
This object can be achieved by means of an apparatus according to the present invention for producing titanate nanostructures by means of alkali-hydrothermal process starting from titanium containing base material, the apparatus contains at least a vessel to be closed by a closure cap and said vessel is rotatable around an axis, and a mixing device arranged inside the vessel, and a heating means is provided, wherein the centreline of the axis is a line penetrating through the vessel, and said mixing device is at least one rod freely movable inside the vessel.
The centreline of said axis is preferably a line parallel to the axis of symmetry of the vessel.
The vessel is advantageously cylindrical and the centreline of said axis is the axis of symmetry of the vessel.
In a preferred embodiment the centreline of the axis is the shorter axis of symmetry of the vessel, and a sleeve is attached to the outer surface of the vessel, and the axis is releasably fixed to the sleeve, and said releasable fixing is a bolt connection.
In a most preferred embodiment cylindrical rods are arranged in the vessel, and said rods are different in size.
Advantageously, said rods are different in length, and the diameter of a rod longer than an other rod is less, than the diameter of the other rod. At least the surface of the rods are made of Teflon (polytetrafluoroethylene) material.
In a particular embodiment of the apparatus according to the invention the heating means is arranged inside the vessel. In an other preferred embodiment the heating means is arranged outside the vessel, and most advantageously, the heating means is a heated chamber and the vessel is arranged in this heated chamber.
The inner surface of the vessel is preferably provided by a coating layer, and said coating layer is made of Teflon material, or said vessel is made of Teflon material.
In a preferred embodiment of the apparatus according to the present invention said vessel is provided by two sleeves along the centreline of the axis, and axes are attached to both sleeves.
The invention will now be disclosed in details in reference of the drawing attached. In the drawing

Fig. 1.: is a sectional elevational view of the apparatus according to the invention, and
Fig. 2.: shows a preferred embodiment of the mixing devices arranged in the reaction vessel.

A particular embodiment of the apparatus according to the present invention is shown in Fig. 1. The apparatus is suitable for producing titanate nanostructures by means of alkali-hydrothermal process starting from titanium containing base material. The apparatus contains at least a vessel 1 to be closed by a closure cap F and said vessel 1 is rotatable around an axis T. The vessel 1 is preferably cylindrical and the centreline k of said axis T is the axis of symmetry of the vessel 1. In the embodiment depicted the closure cap F is fitted to the vessel 1 by means of a thread, and it is secured against rotation to an inner cap 4 by means of clamping screws. The closure cap F may be formed and secured by means of other known solutions, indeed. Vessel 1 is a cylindrical container in the embodiment shown, having a shell 5, and a coating 2 is arranged on the inner surface thereof. Mixing devices 3 are arranged inside the vessel (1), which are independent of the structure of the vessel 1 and freely movable inside the vessel 1.
It can be seen in the drawing, that the centreline k of the axis T is a line penetrating through the vessel 1, and in this embodiment it is aligned with the shorter axis of symmetry of the vessel 1 having cylindrical shape. Preferably, the centreline k of the axis T is a line parallel to the axis of symmetry of the vessel 1, but in a further possible embodiment (not shown) centreline k of the axis T penetrating through the vessel 1 is not parallel to the axis of symmetry of the vessel 1, but it is parallel to or aligned with a line designated by k1, k2, k3 or any line kn penetrating the vessel 1.
A sleeve P is attached to the outer surface of the vessel 1, i.e. by welding, or in the case of a cast (cast iron) shell 5, by means of casting-in. The axis T is releasably fixed to the sleeve P, preferably by means of bolt connection. Any other known bonding unit may equivalently be suitable, indeed.
We have found that in lack of mixing devices 3, in a less extent due to the axis arrangement according to the invention, but similarly to the solution disclosed in JP 2006089307 , the product partly set into an inhomogeneous and hard layer at a place of the vessel 1 distant from the axis T. However, we have recognized that due to the axis arrangement and to the use of inner mixing devices 3 a soft, loose and foamy product can be obtained, even by using as high as 135 rpm or higher number of revolution, if the inner mixing devices 3 cannot "set" along with a sediment because of the centrifugal force. This condition can not be accomplished by using "dumpy" mixing means like balls, since this type of means are "set" just over 5 rpm on the surface of the vessel 1 placed in the direction of the centrifugal force.
Consequently, the mixing device 3 must be at least one rod like element arranged in the vessel 1. The rod like mixing devices 3 placed in the vessel 1 are preferably of cylindrical shape, among which there are rods 3 having different sizes. However, the cross sectional area of the rods 3 can be various, i.e. polygonal, rather than a circle, and their base plate is preferably plane. Rods 3 shown in Fig. 2. are different in length, and the diameter of a rod 3 longer than an other rod 3 is less, than the diameter of the other, shorter rod 3. The number of rods 3 is i.e. three. The set of rods 3 shown in the Figure 2 contains three rods 3 of different sizes. For example, the length L1 of the longer rod 3 is preferably 90% of the height M of the vessel 1, and its diameter D1 is 8% of the diameter D of the vessel 1. The rod 3 in the middle has a length L2, which is preferably 80% of the height M of the vessel 1, and its diameter D2 is 10% of the diameter D of the vessel 1. The length L3 of the shortest rod 3 is preferably 60% of the height M of the vessel 1, and its diameter D3 is 16 % of the diameter D of the vessel 1. Naturally, an arbitrary number of rods 3 might be used provided that their free movement is possible during rotation of the vessel 1.
The role of the rods 3 increases while the number of revolution is increasing. Since rods 3 can move freely, they alter the flow pattern at every revolution of the vessel 1 and prevent particles from setting due to the centrifugal force, on the one hand, and on the other hand they break up the crust possibly formed and return the particles into the suspension.
Apparatus according to the present invention is provided with a heating device H creating and maintaining a temperature necessary to proceed the reaction inside the vessel 1. Heating means H can be arranged inside the vessel 1, i.e. in the form of an electric heating wire arranged between the shell 5 and the coating 2 and provided by electric supply through a sliding contact. In a more preferred embodiment the heating means H is arranged outside the vessel 1, i.e. in a chamber K of a furnace having adjustable heating.
In a preferred embodiment vessel 1 is provided by two sleeves P along the centreline k of the axis T that is on both opposite sides of the vessel 1, and axes T may be attached to both sleeves P. In this case it is possible to rotate more than one vessel 1 around the centreline k, increasing the effectiveness of the apparatus. The axis T can be rotated by any known way, preferably by an electric engine E.
Beyond producing titanate nanostructures, the apparatus according to the present invention is suitable for synthesizing vanadic-oxide, copper, copper-oxy-hydroxide, zincoxide, iron-oxide, silica, alumina, cadmia, potassium-niobate, manganic-oxide, bismuthtelluride, bismuth-vanadate, selenium, tellure, silver, tungsten-sulphide, cadmium-hydroxide, lead-sulphide, bismuth-sulphide, zinc-sulphide, nickel sulphide and bariumtitanate nanostructures (nanotube and/or nanofibre).
The apparatus according to the present invention for producing titanate nanostructures using rotation necessary to decrease diffusion limit, decreases or eliminates sediment forming effect of the rotation, thus a simple and inexpensive apparatus is provided, which is suitable for producing principally titania nanofibres being longer and having more uniform morphologic parameters than the known nanofibres, and the product has loose and foamy consistency rather than a hard sediment, even by high speed of rotation.

Claims

Apparatus for producing titanate nanostructures by means of alkali-hydrothermal process starting from titanium containing base material, the apparatus contains at least a vessel (1) to be closed by a closure cap (F) and said vessel (1) is rotatable around an axis (T), and a mixing device arranged inside the vessel (1), and a heating means (H) is provided, characterised in that the centreline (k) of said axis (T) is a line penetrating through the vessel (1), and said mixing device is at least one rod freely movable inside the vessel (1).
Apparatus according to claim 1., characterised in that the centreline (k) of said axis (T) is a line parallel to the axis of symmetry of the vessel (1).
Apparatus according to claim 2., characterised in that the vessel (1) is cylindrical and the centreline (k) of said axis (T) is the axis of symmetry of the vessel (1).
Apparatus according to claim 3., characterised in that the centreline (k) of said axis (T) is the shorter axis of symmetry of the vessel (1).
Apparatus according to claim 4., characterised in that a sleeve (P) is attached to the outer surface of the vessel (1), and the axis (T) is releasably fixed to the sleeve (P).
Apparatus according to claim 5., characterised in that said releasable fixing is a bolt connection.
Apparatus according to any claim of 1.-6., characterised in that cylindrical rods (3) are arranged in the vessel (1).
Apparatus according to claim 7., characterised in that said rods (3) are different in size.
Apparatus according to claim 8., characterised in that said rods (3) are different in length, and the diameter of a rod (3) longer than an other rod (3) is less, than the diameter of the other rod (3).
Apparatus according to claim 9., characterised in that at least the surface of the rods (3) are made of Teflon (polytetrafluoroethylene) material.
Apparatus according to claim 10., characterised in that the heating means (H) is arranged inside the vessel (1).
Apparatus according to claim 10., characterised in that the heating means (H) is arranged outside the vessel (1).
Apparatus according to claim 12., characterised in that the heating means (H) is a heated chamber (K) and the vessel (1) is arranged in the heated chamber (K).
Apparatus according to any claim of 1.-13., characterised in that the inner surface of the vessel (1) is provided by a coating layer (2).
Apparatus according to claim 14., characterised in that said coating layer (2) is made of Teflon material.
Apparatus according to any claim of 1.-13., characterised in that said vessel (1) is made of Teflon material.
Apparatus according to any claim of 1.-16., characterised in that said vessel (1) is provided by two sleeves (P) along the centreline (k) of the axis (T), and axes (T) are attached to both sleeves (P).