DE3890597C2 - Decomposition of organic chemicals with ceramic titanium membranes - Google Patents

Description

The present invention relates to the use of kera mix membranes and especially the reliable and he consequent use of both fine and poly meren ceramic titanium membranes and coatings for Zer settlement of permanent organic compounds.

Ceramic membranes are currently used in industry and Science for a variety of processes and purposes turns, of which the most common separations are. Although most commonly used organic membranes for separation processes ceramic membranes enjoyed several Advantages that they have over organic membranes increasing popularity. Ceramic membranes are one size  re chemical stability as it is against organic solutions medium, chlorine and extreme pH values are stable. Kerami cal membranes are stable even at very high temperatures, what an efficient sterilization of process equipment gene and pharmaceutical equipments allowed with orga African membranes is often not possible. Because ceramic mem industries are inorganic, they are generally quite sta against microbial or biological decomposition, which in organic membranes can occasionally be a problem. Ceramic membranes are also mechanical even under high ones Press very stable. The temperature, the chemical and mecha The stability of ceramic membranes allows them to be effective easier to clean than less permanent membrane assembly tongues.

The mode of operation and types of separation with ceramic mem Branches that can be reached are generally from Asaeda et al., Jour. of Chem. Eng. of Japan, 19: 1, 72-77 (1986) dis cut. At least one product line is currently kera mixer filters on the market that are marketed under the trade name "Ceraflo" from Norton in Worcester, Massachu setts, is marketed.

Although many of these properties are inorganic membranes seem to favor organic membranes The use of these membranes in a variety of commercial areas len applications so far because of the difficulty of crack-free mem to produce industries that have a defined pore size and Have a small pore size distribution in desired areas. Some types of prior art inorganic membranes Technique like that by applying particles to one Ultrastabilized zir condensation membranes are stable, but have relatively large ones Pore sizes that they only use for separations at very high moles Make the eyepiece weight suitable.  

The influence of temperature and light intensity on photocatalytic decomposition of 3,4-dichlorobiphenyl adsorbed on TiO₂ surfaces has already been investigated the as described by S. Tunesi and M. Anderson in Photocatalysis of 3,4-DCB in TiO₂ aqueous Suspension: effects of temperature and light intensive CIR-FTIR interfacial analysis, 16 Chemosphere 7, 1447, (1987). Aqueous titanium dioxide Suspensions used. It has been shown that an increase in intensity, i. H. the number of photons, the decomposition of the or ganic connection much more favored than one of the increased intensity over this period of time energetically corresponding temperature increase of the aqueous titanium di oxide suspension.  

There has been considerable effort in the creation of metal oxide membranes inserted using aluminum. So For example, it has been shown that the use of sol-gel Techniques the reproducible production of ceramic Alumina membranes are allowed to be supported or free could be; LeEnaars et al., Jour. of Membrane Science, 24, 261-270 (1985). It has been shown that by the controller various process parameters reliable processes for Creation of ceramic alumina membranes with relative fine pores and a reliable size distribution of the buttocks can be developed.

The knowledge in this field for the production of ceramic Titanium dioxide membranes have so far been limited. The most of Sol-gel techniques using titanium fell on the Production of very thin, finely divided films because of their op table and corrosion-resistant properties. Nevertheless are the different parameters for reproducible and uniform production of these or similar films are not yet in any way necessary have been written that they are easily repeatable.

It was recognized some time ago that many are toxic organic chemicals on suspended hydrated oxide particles can be decomposed. The previous research tended to rely on easily decomposing connections, like acetate, and on the use of suspended part to concentrate on the decomposition of such compounds. For example, there are teachings in the prior art on ver Use of suspensions of titanium dioxide particles for decomposition complex organic molecules. The use of the however, suspended particles for these processes is a serious limitation because solid substrates indicate are easier to use. Nevertheless pose completely solid substrates not enough surface for an effective Catalysis ready in acceptable time frames.  

It is therefore an object of the invention to provide a method for simple and effective To provide decomposition of complex organic substances.

This object is achieved by the method according to claim 1.  

Further aims, advantages and characteristics of the present inven dung become clear from the description below.

The present invention is based on the use of titanium oxide membranes for the decomposition of organic molecules directed. Regarding the manufacturing methods of titanium Membranes are of two types. The first variant leg stop the gelation of a colloidal sol. This first Variant uses a gel type that is generally fine is lig, but be formed into a coherent mass can, if the process variables are carefully controlled that, and after gelation to a consistent and equal shaped membrane can lead. The second process variant involves the hydrolysis of an organometallic titanium compound formation to form a soluble intermediate, the then condensed to an inorganic titanium polymer. Because it for catalysis it is desirable that the ver available surface is maximized is porous or fine Partial titanium membrane for the inventive method be prefers.

The process therefore includes the production of a fine one-piece gel, which is then fired to make a ceramic  Get material. There are four in this procedure individual variables that need to be carefully controlled. The first is the ratio of water to titanium in the colloi dalen Sol so that the gel is properly formed. The Ver Ratio is preferably less than about 300: 1, water: Ti tanatoms, on a mole basis. The second criterion is the rich selection of an alcoholic solvent. The alko holic solvent is preferably an alkyl alcohol, of the alkyl radical in the titanium used as the starting material alkoxide is different. The third consideration concerns the tight pH control of the colloidal mixture. This pH Control limits the availability of free protons rela tiv to the titanium molecules. The fourth consideration concerns the upper limit of the sintering temperatures to which the resul be exposed to gel during firing. Brenn temperatures above about 500 ° C can lead to an unan acceptable number of cracks in the resulting ceramic ren.

The production of a finely divided titanium membrane begins a titanium alkoxide. The titanium alkoxide is first at Room temperature hydrolyzed. The typical reaction is that to:

TiR₄ + 4H₂O → Ti (OH) ₄ + 4R.

The radical R can be any alkyl, but it has been found that titanium tetraisopropoxide, Ti (iso-OC₃H₇) ₄, a convenient end is gear.

The titanium alkoxide is first in an organic alcohol solved. It has been found that hydrolysis by Ver use of an alkyl alcohol solvent in which the alkyl is different from alkyl in titanium alkoxide, is facilitated, for example with ethanol and titanium tetraisopropoxide. water  is then in proportions in a total volume from 200 to 300 times, on a mole basis, of the titanium present. The resulting titanium hydroxide, Ti (OH) ₄ falls from the Lö solution.

The titanium hydroxide precipitate will then, again at room temperature, dissolved with HNO₃. This step changes the Precipitation into a highly dispersed, stable, colloidal Solution or a sol um. This suspension is made by stirring for about 12 hours with moderate heating (85 to 95 ° C) Support for colloid formation kept dispersed. To upon cooling to room temperature the colloid gels. The Gel can be on a support such as glass or an optical company water, be solidified or deposited in forms or in Form of foils can be layered to self-supporting structure manufacture doors. The gel is then at a firing temperature ture of no more than about 500 ° C to obtain a dry fired hard ceramic. Higher firing temperatures can cause the membrane to tear. The result is a high porous continuous tissue of sintered particles, the form a rigid membrane.

The resulting ceramic titanium membrane works as highly desirable substrate for the photocatalyzed decomposition organic molecules. The surface of the membranes is highly porous, making it easy to absorb organic molecules will. The titanium molecules are effective for catalytic purposes readily available. Catalysis is by UV light and broad-spectrum UV radiation is actuated, even sunlight usable, although intense artificial UV light into one Can increase the rate of decomposition.

example 1 a) Production of fine-particle membranes

Titanium tetraisopropoxide was obtained from the Aldrich Chemical Company based. The water used for the reactions was under Using a Milli-Q water purification system from Milli pore corporation deionized.  

A series of experiments on hydrolysis and gel formation particles were made using a variety of pH values and relationships between the water concentration tion and the titanium ion concentration. The he Results are summarized in Table 1 below.

Table 1

From the data given above it is clear that the stable Titanium sols can best be achieved if the molar ratio nis from free hydrogen ions (from acid) to titanium  molecules is between 0.1 and 1.0. This area can only in relatively dilute target solutions, such as those of the group B of the table. The reason for this is not fully understood, but can stood between the particles in more dilute solutions lie, which makes aggregation more difficult than in concentrating ten Solen does. Only stable brine can then go through properly Evaporate into coherent transparent gels and then through Protolysis can be converted into coherent oxide membranes.

The acid was found to be the volume of gelation influences. The gel volume goes through a minimum if the acid concentration about 0.4 mol of free protons per Mole of titanium is. The brine must have at least 4.5% of its original weight, depending on the electrolyte concentration, lose to get to the gel point. The brine need about another 97.6% of their original weight lose to form the final solid gel. Heating the end gel in the sintering process leads to another Ge weight loss of about 13.5% without the internal gel structure to destroy.

b) degradation of PCB on the carrier-protected TiO₂ Membranes

To reduce the presence of TiO₂ particles in solution as a result of edge solution the glass-supported membrane previously stirred overnight in distilled water. The 3,4- Dichlorobiphenyl (3,4-DCB) (0.05 mg from hexane solution) added to the membrane by allowing the solvent to evaporate leads. The membrane was then distilled in 50 ml Milli-Q Submerged water and then in a cylindrical pyrexbe given more. The temperature influence on the decomposition of 3,4-DCB adsorbed on TiO₂ particles is already under been searched.  

Therefore a constant temperature of 60 ° C for the Ex experiments selected. The temperature was determined by immersion the Pyrex vessel in a thermostatted water bath con kept constant. The irradiation was carried out with a UV High intensity light source, a Xe-Mg lamp, such as one LPS 200 from Photo Technology International. A comparison experiment was carried out under dark conditions. After 5 hours of irradiation, the 3,4-DCB with a (100: 100 ml) hexane / acetone mixture soxhlet extracted. The Feine was extracted from 5 ml of water with hexane (5 ml x 4). A gas chromatographic analysis was used to determine the con concentration of the organic components with a Hewlett Packard 5730 gas chromatograph equipped with an EC Detector and a capillary column. The percent proportion of decomposition was calculated, the dark Experi ment was assumed as a comparison with zero decomposition. The maximum observed decomposition on the membrane was 93%, during the decomposition in water, as a result of the Ab sorption of organic components on fine TiO₂, 75% scam. The weight recovery of the organic loading components in the dark experiment was, taking into account the amount of orga deposited on the membrane African ingredients, 37%.

c) Decomposition of salicylic acid (SALA) and 3-chlorosalicyl acid (3-ChS) on unsupported TiO₂ membranes

The photocatalytic decomposition of salicylic acid (SALA) was carried out in a photochemical reactor which had a cylindrical arrangement and was placed in the unsupported TiO₂. The reactor was arranged so that the liquid circulated around a Hanovia UV-Hg radiation lamp. The temperature was controlled by a circulating water jacket. A color filter, 5 × 10 ^-2 M NaVO₃ and 5% NaOH, was circulated between the UV lamp and the suspension to reduce the UV transmission at 340 nm to reduce the direct organic photo decomposition. It had previously been found that salicylic solution after 4 hours at a temperature of 45 ° C showed a 25% decomposition compared to a 25 micromolar starting solution.

The photocatalysis of SALA was carried out at pH 3.7 and a temperature of 29 ° C. The TiO₂ membrane had been fired at 375 ° C. 5 ml of 20 mM SALA was added to 700 ml of the solution, the pH of which had been equilibrated overnight. After adding the SALA, the suspension was equilibrated for one hour, which was known from kinetic experiments as sufficient time to reach equilibrium. The SALA concentration in the equilibrium solution was determined to be 88 × 10 ^-6 M by ultrafiltration with a Nucleopore 0.05 micron membrane. The solution was then irradiated for 3 h 40 min, the SALA concentration measured again and determined to be 0.6 × 10 ^-6 M or 0.7% of the initial concentration.

A similar reaction was carried out with 3-chlorosalicylate (3-ChS) carried out in the same reactor type. After 3 h at 25 ° C. the degree of decomposition for 3-ChS to about 90% of the initial con center determined.

It is understood that the invention is not based on the here Explanation given special materials, structures and process is limited, but modified forms including as defined by the following claims be included.

Claims (4)

1. A process for the decomposition of organic molecules on titanium dioxide surfaces, which comprises the following steps:

• a) exposing organic molecules in solution to a titanium dioxide surface, the organic molecules coming into contact with the surface;
• b) irradiating the titanium dioxide surface with ultraviolet light, the organic molecules being decomposed by the ultraviolet light under the catalytic action of the titanium dioxide surface,

characterized in that the titanium dioxide surface is the surface of a ceramic porous titanium membrane. 2. The method according to claim 1, characterized in that the organic molecules are polychlorinated biphenyls. 3. The method according to claim 1, characterized in that in step a) the organi molecules in solution are absorbed by the membrane.