Photochemical reactors are treatment technologies that have emerged in the past 20 years. In sufficient reaction time, organic matter can be completely mineralized into simple inorganic substances such as CO2 and H2O, avoiding secondary pollution. The photochemical reactor is simple and efficient, and has a promising future. . The photocatalytic oxidation method using titanium dioxide powder as a catalyst has the problem of separation and recovery of the catalyst, which affects the practical application of the technology. Therefore, the photochemical reactor is fixed on some carriers to avoid or more easily cause the separation and recovery technology. A wide range of interests of scholars at home and abroad.
I. Research Status of Photochemical Reactor Technology At present, there are two main researches on photochemical reactors at home and abroad. The first type is a non-filled fixed bed type fixing technology, which directly deposits a catalyst on the inner wall of a photochemical reactor by sintering or deposition method, and is pump-powered for sewage treatment, and the photochemical reactor enables the sewage to react with the photocatalyst in the sewage tank. The reflux is circulated between the devices, and the photocatalytic reaction is carried out in the reactor. For example, Zhang Pengyi et al. studied the photocatalytic degradation of benzoic acid. The photochemical reactor has TiO2 fixed as follows [1]: two 120W high pressure mercury lamps are used to illuminate the aluminum plate, while the acidic suspension containing TiO2 powder is continuously circulated. Over the irradiated aluminum plate, TiO2 in the photochemical reactor suspension is deposited on the aluminum plate under the action of ultraviolet light and acidic conditions to form a fixed film. The second type is a fixed type of fixed bed type [2]. The photochemical reactor sinters TiO2 on the surface of a carrier (such as sand, silica gel, glass beads, glass fiber, etc.), and then fills the above particles into the reactor. Although such a fixing technique can increase the contact area of ​​the photocatalyst with the liquid phase (the reaction rate is higher than that of the suspension type photoreactor), the photochemical reactor but the carrier particles are small, and a complicated separation and recovery process is required [3] ].
Second, photochemical reactor immobilization technology research
1. Mechanism discussion Some studies have shown that photochemical reactor is a kind of catalyst fixing technology similar to unfilled fixed bed type, that is, the glass fiber loaded on the bottom of the reactor and loaded with TiO2 film is surface-modified (supporting some surface on TiO2 surface) Some heavy metals or metal oxides, photochemical reactors such as Ag, Au, Pt, Pd, Nb, RuO2 and Pt-RuO2, etc.) can enhance the photocatalytic activity of TiO2. Considering that this technology is used for deep purification of drinking water, the low metal content does not work. The high photochemical reactor content makes the heavy metal content in the water exceed the drinking water standard. Therefore, the author tries to improve the adsorption capacity of TiO2 from another angle. To study the immobilization of the catalyst.
Photochemical reactor activated carbon has been widely used in water treatment because of its large specific surface area, strong adsorption capacity and good hydrophobic properties. The author uses the advantage of activated carbon to improve the photocatalytic degradation performance of the fixed catalyst. The photochemical reactor is to fix the TiO2 powder together with the powdered activated carbon on the inner wall of the reaction vessel, and then carry out the deep treatment test on the tap water. For comparison, pure TiO2 was tested at the same time.
For comparison purposes, the photochemical reactor was tested under different process conditions. One is to replace the inner wall of the reactor with kraft paper, fix the catalyst on the side of the kraft paper, and lining the corresponding size of kraft paper on the inner wall of the reactor according to the required amount of catalyst for testing. The photochemical reactor was directly tested with TiO2 powder as a catalyst, and the treated water was suction filtered with a 0.45 μm filter. The test device is shown in Figure 1. The photochemical reactor is made of glass, the size is 6 × 56cm, the volume is 1582cm3, the actual volume (excluding the UV lamp) is 1287cm3; the power of the quartz ultraviolet germicidal lamp is 20W, the main wavelength of the photochemical reactor At 253.7 nm, the light intensity E is 3.90×103 μW/cm 2 under the conditions of the test; the effect of the air pump is to provide air in addition to aeration to promote the suspension of TiO 2 in the solution, and the actual photochemical reactor is utilized in the air. O2 is an oxidant as an electron acceptor, preventing the recombination of electrons and holes.
2. Preparation of catalyst film The materials required for the photochemical reactor test are as follows: TiO2 (analytical grade); powdered activated carbon (sorted by a 140-mesh fine sieve to make it substantially the same size as the TiO2 powder); commercially available kraft paper; glass glue; Glue gun; scraping board.
First, evenly apply a thin layer of glass glue on one side of the kraft paper (the purpose is waterproof), leave it at room temperature for one night, wait until it is dry after the photochemical reactor, and apply a thin layer of glass glue on the other side before it is dry. A certain amount of TiO2 powder or a complex photochemical reactor catalyst mixed with powdered activated carbon is evenly sprinkled thereon as much as possible, pressed to make it adhere, left at room temperature for a day and night, and after being dried, the remaining powder is weighed, thereby The amount of catalyst possessed by 1 cm2 of kraft paper was calculated.
3, test results and analysis Photochemical reactor for the convenience of comparison, prepared three catalyst membranes, one is a composite catalyst membrane (TiO2 / C), wherein the mass ratio of TiO2 to powdered activated carbon is 3:7, the amount of TiO2 is equivalent during the test At 0.6g / L; the other photochemical reactor is a pure catalyst membrane, the amount of TiO2 is equivalent to 1.2g / L when tested; the third is a pure carbon powder membrane.
From the UVA (ultraviolet absorbance) removal rate, the TiO2/C film is superior to the TiO2 film in the first 90min of the photochemical reactor reaction, and the TiO2 film removal effect is not as good as the UV irradiation at 120min. For the analysis of the reasons, two sets of experiments were carried out. The first group was the change of UVA removal rate of organic matter in tap water with the concentration of TiO2 in the photochemical reactor by suspension photocatalytic oxidation. The test results show that the photochemical reactor has the best removal effect when the TiO2 dosage is 2g/L. The second set of experiments is a comparison of TiO2/C film with 1.2g/L TiO2 suspension and 2g/L TiO2 suspension.
The removal effect of the composite catalyst membrane with a TiO2 concentration of only 0.6 g/L in the photochemical reactor is equivalent to the removal effect of the suspension with a TiO2 concentration of 1.2 g/L. It can be seen that the powdered activated carbon in the composite catalyst membrane has good adsorption capacity, and the catalytic performance of the photocatalyst TiO2 and its photocatalyst is improved. In the test, it was also found that the TiO2 film doped with powdered activated carbon has strong adhesion to the catalyst and does not enter the solution during the reaction (the reason is related to the adsorption of the carbon powder). The photochemical reactor uses this property to prepare adhesion. And a composite catalyst membrane which is excellent in catalytic properties. However, compared with the curve C of Fig. 4, the UVA removal rate of the composite catalyst film is far from the removal effect at the optimum TiO2 dosage (the removal rate is still nearly 20% difference). There are three possible reasons for the summary: 1 The photocatalytic reactor used in the composite catalyst membrane has a TiO2 concentration of 0.6 g/L, which is much smaller than the optimal titanium dioxide dosage (2 g/L); 2 the photochemical reactor is in the composite catalyst membrane. There must be an optimal ratio between TiO2 and carbon powder, so that both adsorption and catalytic performance can be fully utilized. This time, only the composite catalyst film with TiO2:C of 3:7 was tested, so this is not certain. The ratio is the optimal ratio; 3 Photochemical reactor in the preparation process of the catalyst film, in order to remove the film surface does not adhere or adhere to the powder, first wash it under the tap water several times, and soak it in tap water Overnight, the above-mentioned operation process of the photochemical reactor undoubtedly causes the catalyst membrane doped with powdered activated carbon to adsorb some organic matter in the tap water, and in addition to removing the organic matter in the water, the part of the adsorbed substance is degraded during the reaction, and the photochemical reactor and the substance are Not counted. For the above reasons, the composite catalyst film does not achieve the best TiO2 dosage removal effect, but the photochemical reactor has a significant advantage over the pure catalyst membrane. If the above problems are solved (such as increasing the composite catalyst membrane) The amount of catalyst attached, the photochemical reactor selects an optimal ratio of TiO2 to carbon powder), the removal effect of the composite catalyst film is to achieve the best removal effect under TiO2 dosage.
In order to confirm whether the degradation rate of the TiO2 film doped with powdered activated carbon in the photochemical reactor is improved by simple activated carbon, a comparative test was carried out;
The UVA removal rate of the pure activated carbon membrane in the photochemical reactor is not much different from that of the pure ultraviolet irradiation. It can be seen that the activated carbon can only exert its adsorption and catalytic properties when combined with TiO2. The photochemical reactor and powdered activated carbon combined with TiO2 film have better adhesion and removal efficiency than pure TiO2 film. Photochemical reactor technology has found a more ideal composite catalyst and its engineering application method.
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