Reactor and method for treating fluids by using photocatalysts coupled with phosphorescent solids

Description of the Prior Art

Photocatalysis is an effect that occurs when using an electrical semiconductor reactive substances is brought into contact. By the irradiation will be then a doctorate in an energetically higher conduction band. Back remains a hole". The excited electron and / or the hole can be filled with molecules or Radicals on the surface of the semiconductor, z. B. redox reactions, received. So in the presence of oxygen, most organic molecules, To completely oxidize bacteria and viruses.

There are already applications for the purification of water and gases (Bahnemann, Detlef: Photocatalytic Detoxification of Polluted Waters, in the Handbook of Enviromental Chemistry, O. Hutzinger (ed.) Vol. 2 .: Reactions and Processes, Part L: Enviromental Photochemistry, P. Boule (Ed.), Springer Verlag Heidelberg <b>1999</b>. <b>285-351</b>). The most commonly used photocatalyst is TiO₂, With a Energy gap of 3.2 eV he can with ultraviolet light with a wavelength less than 385 nm are activated. But there are also many other photocatalysts with partially lower energy gap. These can be larger with light Activate wavelength. It has recently been involved in the development of Photocatalysts worked with a variety of properties. In particular, in In this context, as an energy stimulus, the area of ​​visible light (Lettmann, Christian: "Conventional and combinatorial development of mixed oxides for photocatalytic water purification with visible light ", Diss. Univ Saarlandes, 2001) and the use of sunlight (EP 0 812 619 A1) mention.

Various types of reactor are described in the literature.

Widely used is the "web plate reactor" in which the treated Fluid meandering over a photocatalyst coated surface flows (EP 0 738 686 A1). The catalyst is irradiated through the fluid, including in the described case of a wastewater treatment Sunlight as an exciter and TiO₂ as Catalyst is described. As a variant, the catalyst is described in the To suspend fluid and separate again after passing through the device. These devices have an extremely high footprint.

There are described cartridges that contain the catalyst and from to flowing through the fluid to be treated. The lighting is done with lamps, the side attached to the cartridges (WO 96/36565). This apparatus has one comparably high space requirements as the "multi-plate reactor".

The "ball pile reactor" consists of glass beads. which is coated with catalyst are and through the interstices, the fluid flows (WO 95/11751). The Irradiation is carried out by lamps, which are introduced into the bed. Most Application as a fixed bed, but also as a fluidized bed. Disadvantage is that an increased Packing density with only small penetration depths of the radiation must be bought.

In suspension reactors is a finely divided catalyst with variously arranged lamps irradiated (EP 0 233 498 B1). Due to the strong shading by other catalyst or reagent particles is only ever a very small part of the existing catalyst surface activated, if not with strongly diluted catalyst solutions and correspondingly low conversion is working.

Arrangements are described in which the light through glass plates for Photocatalyst is transported (WO 97/37936). Space requirements and complex Construction correspond to the web plate reactors described above.

In WO 98/17390 is an arrangement with many thin glass slides described. They carry the catalyst on their surface. The irradiation is carried out by Lamps, the annular stack of glass plates by means of Penetrate recesses in the glass plates. The construction is very filigree and complicated.

Disadvantages of the prior art and resulting requirements

All known reactor designs have in common that they only a very small Achieve packing density of the irradiated catalyst surface. This does the Apparatus expensive. In addition, they often have a significant footprint, as well the application is more expensive.

The slightly more compact known types are very filigree and intricately constructed and therefore expensive.

In these circumstances lies the real reason that makes photocatalysis hitherto has not enforced on an industrial scale.

It was therefore the object to develop a method and devices, the highest possible packing density of the irradiated catalyst surface with connect the most cost-effective construction and operation.

This object is solved by the features of the main claims and by the promoted the dependent claims.

Transport of energy by phosphorescent substances

The invention is based on the novel principle, the necessary energy Phosphorescent substances in the vicinity of the photocatalytically active surface (im following photocatalyst called PK) to transport, where the phosphorescent particles emit light of suitable wavelength and activate the PK.

The phosphorescent particles (called micro-radiators MR below) must be "charged" to a suitable light source. They will then become photocatalytically active layer transported where they stored their give off all or part of electromagnetic energy, and then back to the UV light source to get. etc.

This has the advantage that, if suitable MR, the stored energy with a half-life of a few seconds to minutes inside the Reaction room to the PC, where they exert their catalytic effect can, while due to the short half-lives of the active state of PK otherwise they only react near the source of energy.

As reactors come different types of reactors that are responsible for reactions and / or for Substance transport processes can be used, in question, preferably: <ul><li>- Fluid bed, fluid bed cascade, gutter</li><li>- Spouted Bed, Cascade from Spouted Beds</li><li>- loop reactor, cascade of loop reactors</li><li>- stirred tank, stirred tank cascade</li><li>- tubular reactor</li><li>- Fixed bed (with PK coated) or all open, ordered structures like Platelets, honeycombs, etc.</li></ul>

In all of these methods, the MR are activated at a light source, physically mixed with the reaction solution and the PK, after giving the energy to the PK returned to the light source, "charged" and fed back to the catalyst.

The mixing can be due to currents and particle diffusion in the Apparatus done. If these transport mechanisms are sufficient, then the light source can z. B. a UV lamp (s) installed directly on the wall of the apparatus or in the apparatus allowing the nearby high-density MR to pass be charged by the flow back into the interior of the reactor reach.

In addition, by baffles, baffles, agitators, etc. these Transport mechanisms are improved.

Alternatively or additionally, the MR can be connected via an external circuit to suitable Lamps are passed. For this purpose, preferably the MR from treated fluid and separated from the PK to its concentration at the light source increase and avoid shading by PK and substrate particles. Preferably, the MR with a small amount of the fluid to be treated convective transported.

The most commonly used photocatalyst is TiO₂, With an energy gap of 3.2 eV he can with ultraviolet light with a wavelength less than 385 nm to be activated. But there are also many other photocatalysts known with light of wavelength greater than 385 nm. As examples are here called ZnO and the oxides of other transition elements (WO 95/11751) and CdS [EP 0 234 875 B1] and SnO₂, SrTiO₃, WHERE₃, Fe₂O₃ (WO 96/36565). The series of Examples could be continued.

Recently, photocells have been used for the visible light range (Lettmann, Christian: "Conventional and Combinatorial Development of Mixed oxides for photocatalytic water purification with visible light ", Diss. Univ. Saarland, 2001) and for the use of sunlight (EP 0 812 619 A1) developed.

Preferably, relatively hard and abrasion resistant PK are used, wherein inorganic substances which are not oxidized are preferred. Depending on the type of use of the PK have very different particle sizes and structures. Suspension catalysts: particle diameter: 1 nm to 100 μm Fluidized bed reactor: particle diameter: 1 μm to 1 mm

When using fixed beds (or all reactors with ordered structures such as platelets, honeycombs, etc.), the photocatalyst is more or less thin Layer fixed on the resting support.

The microradiator MR

The microradiator MR is a phosphorescent solid which is in the form of Particles is used. He must have a sufficiently long persistence time (at least in Seconds range, better a few minutes or longer, preferably 5 seconds to 30 minutes) and emit in the wavelength range in which the Photocatalyst can be activated.

Examples of suitable phosphorescent solids

There are many phosphorescent solids with visible emissions Area known that were developed for other purposes but all Cover requirements for the application described here. Instead of a extensive list is referred to the following references, whose Content is hereby incorporated (US Pat. No. 6,287,993, DE 195 21 119 A1, DE 199 26 980 A1, DE 199 34 436 A1).

The application of this MR is done z. In combination with the one in Lettmann, Christian: "Conventional and combinatorial development of mixed oxides for photocatalytic water purification with visible light ", Diss. Univ Saarlandes, 2001, photocatalysts (PK).

In US Pat. No. 6,287,993, there are long luminous phosphorescent substances described. Among others, in Example 17 doped with zinc and praseodymium Described glass which is suitable with an emission of 350 to 450 nm, TiO₂ as photocatalyst to activate (see. <b>FIG.</b> 3).

Also in DE 195 21 119 A1, are "slowly decaying" phosphorescent Substances described as TiO₂Activators can be used as they also emit at below 400 nm. These are glasses that with rare earth metals are doped.

In principle, the grain size spectrum of MR is the same as in photocatalyst PK between 1 nm and 1 mm, preferably 1 μm-0.5 mm, depending on the application.

An efficient and economical solution - preferred for larger appliances - exists The fact that the particle size of the MR is significantly higher than that of the PK, so that at the Lamp "charged" MR particles as many PK particles irradiated. Further this has the advantage that the MR easily through filters or sieves from the fluid and the contained therein PK can be separated and fed to a regeneration.

Another efficient and economical solution - preferred for small appliances - is that the particle size of the MR is significantly lower than that of the PK, so to achieve a simple separation of MR and PK.

In principle, however, no ratio of the particle sizes of PK and MR be excluded. This results from the variety of suitable ones alone Types of apparatus.

Suitable are massive particles that are particularly easy to produce, but also those in which the phosphorescent material on a carrier core is coated. Using a magnetic core opens up additional space Possibilities for separation and transport of MR particles.

Avoidance of abrasion on the MR and / or corrosion and / or dissolution of the MR

To avoid abrasion, the MR, if not out of a glass anyway consists of a (thin) light-transmitting layer (eg glass) coated become. This can also be against corrosion or dissolution of the MR in the treated Protect fluid.

Separation of photocatalyst PK and micro-radiators MR

The separation of PK and MR (also abrasion!) From the fluid can be over classic Methods such as filters, cyclone, centrifuge, etc. but also with MR Magnetic separator (see above) done.

The separation of PK and MR from each other can be determined by the particle size (filter, Zyklon) but also about the density (cyclone, centrifuge) and other physical Differences (eg: magnetic core of the MR, see above) take place.

A preferred method is to use larger MR by means of a bandpass filter of Fluid and PK to separate the separated MR at a high-energy light source to activate and return from the end of the filter belt back into the fluid.

As light sources are particularly UV lamps with the appropriate spectrum for Excitation of micro-radiator particles suitable.

In an external circuit, the lamp is preferably in a special apparatus to install. This ensures by its guidance of the MR particles, that one possible efficient illumination of all MR particles takes place; for example by: Movement of MR particles in a narrow gap around the lamp. Flow with good particle transport across the flow direction (eg in a fluidized bed with built-in lamps or through Expression of a turbulent flow, etc.)

Preferably, the photocatalyst PK from the micro-radiator MR before the disconnected external lamp to shadowing by the PK when "charging" the MR avoid.

Even with direct irradiation in the apparatus is an (at least partial) separation of the PK from the MR in the vicinity of the radiator to prefer (eg over the Flow guidance or upstream filters or magnetic fields when using a magnetic core of the MR).

It goes without saying that the reactor next to the fluid to be treated the necessary reactants must be supplied. (eg: supply of O₂ to Oxidation of organic contaminants in water).

Likewise, usually the reaction products (eg CO₂) behind the reactor from treated fluid to be separated.

Suitability of problem solutions for media and reactions

The inventive method is for all chemical reactions, the photocatalytically active surfaces in liquids or gases can, suitable.

Preferred application finds the invention for the oxidation of dissolved organic molecules, dispersed droplets and particulates, microorganisms and Viruses in water and gases (also gas bubbles in water).

The wavelengths of light to "charge" the MR and the radiation through The MR does not have to be the same. Often the radiated light is boring postponed. The light emitted by the MR should be sufficiently energetic (shortwave) be to apply the necessary catalyst energy (eg UV light).

The term "light" may be more appropriate by the term "electromagnetic radiation Wavelength "is thus also valid for other wavelength ranges Use of appropriate photocatalysts (especially visible light or sunlight).

By using the microradiators MR, a packing density of the irradiated catalyst surface achieved, as with any of the known methods is possible. In addition, quite simple possibly known apparatuses can be used become. They only have to be adapted or modified to the new procedure. Only the appliances that contain the external bulbs may require New designs.

example 1

Laboratory suspension reactor loud

FIG.

1

The reactor consists of the stirring vessel <b>1</b> with paddle stirrer <b>2</b>, a supply line for Oxygen (air) <b>3</b>, a derivative for exhaust gases <b>4</b> and an external lamp (UV radiator) <b>5</b> and contains a suspension of a reaction medium <b>6</b>, as ο shown microradiators <b>7</b> as well as the. represented photocatalysts<b>8th</b>,

The suspension - consisting of 500 ml of an aqueous solution of an organic Stoffs and photocatalyst and micro-radiator MR in a reactor volume of 800 ml is constantly stirred, resulting in a, descending in the center and at the Wall rising flow yields, while a UV lamp (20 Watt power at 350 nm radiation maximum) irradiated laterally (irradiated area 50 cm²). This is how all MR particles come to the UV source on a timely basis, where they are to be activated. Air is passed through in fine pearls.

The addition of micro-radiator MR increases the degradation rate of the organic Component considerably, in which he radiated energy inside the reactor brings.

Example 2

Laboratory suspension reactor with external circulation of the micro-radiator MR loud

FIG.

2

The reactor consists of a stirred vessel <b>1</b> with paddle stirrer <b>2</b>, a supply line for Oxygen (air) <b>3</b>, a derivative for exhaust gases <b>4</b>, being below the stirrer <b>2</b> on sedimentation <b>9</b> is provided, in which the heavier MR <b>7</b> collect, with little fluid <b>6</b> together over the pump <b>10</b> and direction <b>11</b> in the outer annular gap <b>12</b> a UV lamp <b>5</b> and after activation via the line <b>13</b> again from up in the stirred tank <b>1</b> to be returned.

The suspension - consisting of an aqueous solution of an oxidizable Substance, photocatalyst and micro-radiator is constantly stirred and through Passage of air with O₂ saturated. The micro-radiator (0 to 10 g) is used in the Sedimentation space constantly separated from the photocatalyst and at a UV Lamp passed back to the laboratory reactor. The circulation speed is For example. 5 or 10 ml / min. In the outer circuit are z. B. 10 g or at two lamps 20 g additional MR to the amount in the stirred tank. The addition to Micro-radiator increases the degradation rate of org. Substance considerably. That too Increasing the circulating flow rate increases the rate of degradation.

Example 3

Tubular reactor with meandering ribs and separate external circulation of Photocatalyst (PK) and microradiators (MR) loud

FIG.

3

The reactor consists of a tubular reactor <b>21</b> with built in meandering shape arranged, horizontal ribs <b>22</b>from the bottom over the pipe <b>23</b> from the mixer <b>24</b> a mixture consisting of: reaction solution <b>6</b>that with oxygen is enriched and the mixer over the line <b>25</b> is supplied, photocatalyst <b>8th</b>. the over the pump <b>27</b> and direction <b>26</b>/<b>28</b> is circulated and microradiators <b>7</b>that over the wires <b>11</b> and <b>13</b>, the pump <b>10</b> and the UV lamp <b>5</b> surrounding ring coat <b>12</b> be recycled, is supplied, which the reactor via the separator <b>29</b> leaves where it is separated into the components becomes. The reacted reaction solution and formed exhaust gases are on the management <b>30</b> dissipated.

Example 4

Tubular reactor with photocatalyst coated honeycomb installations and external Activation loud

FIG.

4

The reactor consists of the tubular reactor housing <b>1</b> with honeycomb fittings <b>32</b> in the direction of the tube, which are coated with photocatalyst. reaction solution <b>6</b> from the supply line <b>25</b> and activated microradiators <b>7</b> from the Circuit line <b>13</b> be over the mixer <b>24</b> and direction <b>23</b> introduced into the reactor, happen the honeycomb installations <b>32</b> and give off their photo energy to the PK, before they are in the separator <b>29</b> from the solution <b>6</b> be disconnected and via wire <b>11</b> and pump <b>10</b> in the ring coat <b>12</b> the lamp <b>5</b> where they are exposed to UV Light activated and over the line <b>13</b> be recycled back into the reactor.