JP2739128B2 - Decomposition method of organic chemicals by titanium ceramic membrane - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to the use of ceramic membranes, and more particularly, to decompose durable organic compounds.
It relates to the use of both particulate and polymeric titanium ceramic membranes and coatings to produce reliable and good results.

BACKGROUND OF THE INVENTION Ceramic membranes are currently used in industry and science for a variety of manufacturing methods and purposes, of which separation is the most commonly used. While organic membranes are most frequently used in separation processes, ceramic membranes have become increasingly popular due to some of the advantages that ceramic membranes have over organic membranes. Ceramic membranes have excellent chemical stability because they are resistant to organic solvents, chlorine and extreme pH. Although ceramic membranes are also stable at high temperatures, they can efficiently sterilize manufacturing and formulation equipment, but this is often not possible with organic membranes. Since ceramic membranes are inorganic, they are usually very stable against microbial or biological degradation, which is often a problem with organic membranes. Ceramic membranes are also very structurally stable, even under high pressure. The stability and structural stability of ceramic membranes to temperature and chemicals allows for more efficient cleaning than other less durable membrane compositions.

Asaeda et al. Have comprehensively described the operating mechanisms and separation types achievable with ceramic membranes, Jour. Of Chem. Eng. Of Japan, 19 :
1, 72-77 (1986). Currently, Norton (No
rton Company (Worcester, Mass.) sells at least one line of ceramic filters sold under the trade name "Ceraflo".

Due to many of these features, inorganic membranes seem to be preferred over organic membranes, but it is difficult to produce pore-free and pore-size-distributed membranes in desirable ranges, and it is difficult to produce crack-free membranes. Wide commercial application and use has been slow. Certain types of prior art inorganic membranes, such as ultra-stabilized zirconia membranes made by depositing particles on a silica carrier, are stable, but have a relatively large pore size, resulting in very high molecular weights. Only suitable for separation.

Various attempts have been made to create a metal oxide film using aluminum. For example, it has been demonstrated that supported or unsupported alumina ceramic membranes can be produced with good reproducibility using sol-gel technology. Lenaars et al., Jour. Of Mebrame Science, 24, 261-270.
(1985). By controlling various parameters of the manufacturing method, it has been clarified that a reliable manufacturing method for creating an alumina ceramic film having relatively dense pores and a reliable pore size distribution can be developed.

Until now, knowledge of titanium ceramic membrane manufacturing technology was limited. Most sol-gel knowledge using titanium was aimed at producing very thin particle films with optical properties and corrosion resistance. However, various parameters necessary for continuously producing these films or similar films with good reproducibility have not been strictly described so as to be easily reproducible.

Many toxic organic chemicals are suspended hydroxides (hydrous ox)
ide) It has recently been recognized that it is degradable on particles. Previous work has focused on compounds that break down readily, such as acetate, and the use of suspended particles to break down such compounds. For example, there is knowledge in the prior art regarding the use of titanium dioxide particle suspensions for the decomposition of complex organic molecules. However, the use of suspended particles in these processes is a major limitation,
The reason is that solids are clearly more convenient to use. However, perfect solids do not provide sufficient surface area to promote efficient catalysis in a reasonable amount of time.

(Summary of the Invention)

The present invention provides a method for decomposing complex organic molecules in a solution, comprising the steps of placing a porous titanium ceramic film in a solution containing the molecules and irradiating the titanium ceramic film with ultraviolet light. I do. It is an object of the present invention to provide a simple and efficient method for decomposing complex organic substances. Other objects, advantages and features of the present invention will become apparent in the following written specification.

(Detailed description of the invention)

The present invention is directed to the use of titanium oxide films for organic molecule decomposition. There are two variants of the titanium film manufacturing method. The first variant involves gelling of the colloidal sol. The first variant is usually particulate, but with careful control of the process elements, if it can produce a continuous, uniform film after gelling, it can be cast as a mass. The use of some type of gel. A second variant of this law is:
Including hydrolysis of an organometallic titanium compound, and forming a soluble intermediate, followed by condensation with an inorganic titanium polymer. Porous or particulate titanium membranes are desirable for the process of the present invention, as it is desirable for the catalytic activity to maximize the surface area available for the substrate.

Thus, the process involves the production of a particulate gel, which is then fired to a ceramic. In this process, there are four prominent variables that must be carefully controlled. The first is the ratio of water to titanium in the colloidal sol to properly form the gel. This ratio is preferably such that the ratio of water to titanium atoms is less than 300: 1 (mole: mole), and the second criterion is to properly select the alcohol solvent. The alcohol solvent is preferably an alkyl alcohol different from the alkyl group of titanium alkoxide used as a starting material. A third consideration is the tight control of the pH of the colloid mixture. This pH control limits the availability of free protons for titanium molecules. A fourth consideration is the upper limit of the sintering temperature when exposing the resulting gel during firing. Firing temperatures above 500 ° C. will cause an unacceptable amount of cracking in the resulting ceramic.

The production of a particulate titanium film starts with a titanium alkoxide. Titanium alkoxides are first hydrolyzed at room temperature. A typical reaction is TiR ₄ + 4H ₂ O → Ti (OH) ₄ + 4R This R group can be any alkyl, but titanium tetraisopropoxide Ti (iso-OC ₃ H ₇ ) ₄ is a convenient starting point. It turned out to be raw material.

The titanium alkoxide is first dissolved in the organic alcohol. By using an alkyl alcohol solvent of an alkyl different from the alkyl of the titanium alkoxide,
Hydrolysis is best. For example, ethanol in the case of titanium tetraisopropoxide. Next, a total of 200 to 300 times (mole to mole) water of titanium present is added. The produced titanium hydroxide Ti (OH) ₄ precipitates from the solution.

The titanium hydroxide precipitate is then peptized again with HNO ₃ at room temperature. At this stage, the precipitate is converted into a highly dispersed, stable colloidal solution or sol.
The suspension is moderately warmed (85-95 ° C) for about 12 hours while stirring to maintain dispersion and promote colloid formation.
Upon cooling to room temperature, a colloidal gel forms. The gel may be immobilized on a carrier such as glass or optical fiber, or may be cast. Alternatively, the sheet may be layered in order to have a self-supporting structure. The gel is then sintered at a firing temperature not exceeding 500 ° C. to produce a hard, dry ceramic. At higher firing temperatures, cracking of the film occurs. The result is that a highly porous continuous sintered particle network forms a firm film.

The resulting titanium ceramic membrane functions as a highly preferred substrate for photocatalytic degradation of organic molecules. The membrane surface is highly porous, thereby easily absorbing organic molecules. This titanium film can be easily used for catalytic activity. This catalysis is activated by UV light and broad UV irradiation, and even sunlight can be used. However, high intensity artificial UV light tends to sensitize the decomposition rate. Although the complex organic compound which can be decomposed by the method of the present invention covers a wide range, the method of the present invention is particularly effective for use in decomposing polychlorinated biphenyl.

Example 1 a) Preparation of a particle membrane Titanium tetraisopropoxide was obtained from Aldrich Chemical Company. The water used for the reaction was obtained from Millipore Corporation (Millipore Corporation).
Q) Deionized using a water purification device.

A series of hydrolysis and particle gel formation experiments were performed at various pH
It was performed using the values and ratios between water concentration and titanium ion concentration. The results are summarized in Table 1 below.

From the above data, if the molar ratio of free hydrogen ions (from acid) to titanium molecules is between 0.1 m and 1.0,
A stable titanium sol is best produced. On the table, this range can be extended only with relatively diluted sol solutions, such as those of Group B. I'm not entirely sure why,
It appears to be related to the increased interparticle distance in more dilute solutions, making aggregation more difficult than in dense sols. Only the stable sol can be converted into a monolithic transparent gel by evaporation, and then by protolysis,
It could be converted to a titanium oxide film with an integral structure.

It was found that the acid concentration affected the gel volume. At an acid concentration of about 0.4 moles of free protons per mole of titanium, the gel volume is minimized. Depending on the electrolyte concentration, the sol initially loses about 4.5% of its weight and reaches the gel point. To form the final solid gel, the sol must further lose 97.6% of its original weight. The final gel is heated in a firing operation to further reduce weight by about 13.5% without destroying the internal gel structure.

b) to reduce the TiO ₂ particles present in the solution due to PCB decomposition terminal dissolved on TiO ₂ support film, it was stirred in distilled water glass supported film in advance.
The 3,4 dichlorobiphenyl (3,4-DCB) (0.05 mg from hexane solution) was evaporated and the solvent was added to the membrane. The membrane was then washed with 50 ml of Milli-Cue (Milli-
Q) It was immersed in distilled water and placed in a cylindrical Pyrex container. Temperature effect on the degradation of 3, 4-DCB adsorbed on TiO ₂ particles, S. Tsuneshi (Runesi), M. Anderson (Anders
Effect of temperature and light intensity;; on), the photocatalyst of 3, 4-DCB in TiO ₂ aqueous suspension CIR-FTIR interface analysis, 16 Kemosufea (Chemosphere) 7,14,47 (1987) as disclosed in This disclosure is already incorporated herein by reference.

Therefore, a constant temperature of 60 ° C. was chosen for this experiment. The temperature was kept constant by immersing the Pyrex container in a thermostatic water bath. Irradiation is with a high intensity UV light source, Photo Technology International
This was done with a Xe-Mg lamp such as LPS200 (nternational). Blank experiments were performed in the dark. 5 hours after irradiation,
This 3,4-DCB was subjected to Soxhlet extraction with a mixture of hexane / acetone (100: 100 ml). Use hexane (5mlX
In 4), it was extracted from 5 ml of water. Gas chromatographic analysis was performed using a Hewlett-Packard 5730 gas chromatograph with an EC detector and a capillary column to determine the concentration of organic substances. Experiments in the dark were considered zero reduction controls and percent reduction was calculated. The maximum reduction observed on this membrane was 93%, while the reduction in water due to adsorption on TiO ₂ particles was 75%. Weight recovery in the dark experiment was 37% for the amount of organic matter attached to the membrane.

c) Salicylic acid (SALA) on carrier-free TiO ₂ film and 3-
The photocatalytic degradation of degradation salicylic acid-chlorosalicylic acid (3Chs), made during and has a cylindrical structure in photochemical reactor containing the unsupported TiO _2. The reactor was set up such that the liquid in the reactor circulated around the Hanovia UV-Hg wash light. Temperature,
Controlled by a circulating water jacket. Dye filter (NaVO ₃
(5 × 10 ⁻² M in 5% NaOH) was circulated between the UV light and the suspension to reduce UV transmission at 340 nm to reduce direct organic photolysis. It has previously been found that salicylic acid solutions show 25% decomposition at 25 ° C. for 4 hours over 25 ° C. microMolar starting solutions.

The SALA photocatalyst was performed at a temperature of 29 ° C. at pH = 7.3. This TiO ₂ film was fired at 37.5 ° C. 20mM SALA5
ml was added to 700 ml of solution at pH equilibration overnight. This SAL
After addition of A, the suspension was allowed to equilibrate for 1 hour, which was sufficient from kinetic experiments to reach equilibrium.

The concentration of SALA in the equilibrium solution was
e) Ultrafiltered through a 0.05 micron membrane and measured 88 × 10 ⁻⁶ M. The solution was then irradiated for 3 hours and 40 minutes and the SALA concentration was re-measured and found to be 0.6 × 10 ^-6 M or 0.7% of the original concentration.

Using this same type of reactor, a similar reaction was carried out with 3-chlorosalicylic acid (3-ChS). 3-C at 25 ° C for 3 hours
The hS degradation was found to be approximately 90% of the original concentration. It is to be understood that this invention is not limited to the particular materials, structures, and processes described herein as examples, but also includes modifications of the claims.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tennesee Simonetta 53703 Madison West Gorham Street, Wisconsin, United States of America 138 (72) Inventor Zoo Kunin 53705 Madison Eagle Heights, Wisconsin, United States 803 Ai (56) References 118289 (JP, A) JP-A-59-4436 (JP, A)

Claims (2)

(57) [Claims] 1. A method for decomposing photocatalytically decomposable organic molecules in a solution, comprising the steps of: placing a self-supporting porous ceramic film of titanium oxide in a solution containing the organic molecules; A method comprising irradiating. 2. The method according to claim 1, wherein the organic molecule capable of photocatalytic decomposition is polychlorinated biphenyl.