Flow-through photo-oxidation reactor

Abstract

The present application relates to a flow-through photooxidation reactor, and to a method of treating water having a conductivity of at most 20 µS / cm.

Description

[0001] P24-250

[0002] - 1 -

[0003] FLOW-THROUGH PHOTO-OXIDATION REACTOR

[0004] Technical Field

[0005] 5

[0006] The present application relates to a flow-through photooxidation reactor, and to a method of treating water having a conductivity of at most 20 pS / cm.

[0007] Background

[0008] 10

[0009] Many applications in chemistry (particularly analytical chemistry), biology, pharma or electronic device production (such as the production of semiconductors), require water of a purity higher than natural or tap water. There are several types of water purity available depending on the intended use. For example, the American Society for Testing and Materials (ASTM) uses D1193-06 and distinguishes four grades of water. The highest purity water, often denoted as "ultrapure" or in accordance with ASTM D 1193-06 as "Type I" water, is, for example, characterized by a resistivity of at least 18.0 MQ • cm and at most 5 ppb of total organic carbon (TOC). "Type II" water is typically characterized by a resistivity of at least 1.0 MQ • cm and at most 50 ppb of total organic carbon. "Type III" water is the lowest quality water grade for laboratory use, having a resistivity of at least 0.05 MQ • cm and at most 200 ppb of total organic carbon, and is recommended for standard laboratory use, such as for glassware rinsing or heating baths, as well as a feed to water purification systems producing Type I water.

[0010] 25 Water purification systems capable of consistently providing the user with water of high purity in sufficient volume are already known. Starting from, for example, tap water such water purification systems generally comprise a number of steps or stages, such as reverse osmosis, electrodeionization, ion exchange, filtration (e.g. ultra- and / or microfiltration), activated carbon filter, photooxidation in order to bring the water to the desired quality.

[0011] Organic contaminants have been found to be removable using UV irradiation, such as emitted by low pressure mercury lamps at 185 nm and 254 nm. However, with the use of mercury now becoming more and more restricted, Millipore first used photooxidation reactors comprising an excimer lamp emitting at a wavelength of 172 nm in their Milli-Q®

[0012] 35 IQ 7000 water purification systems. In excimer lamps, emission of UV radiation results from excited dimers spontaneously transiting from their excited state to a ground state. Emission of radiation having a wavelength of, for example, 172 nm is achieved using Xe2* P24-250

[0013] - 2 - as excimer molecule. Other wavelengths may be achieved using different excimer molecules as can easily be found in the general literature.

[0014] Neither mercury nor excimer lamps are designed to be waterproof and in some instances

[0015] 5 also require high voltages. Furthermore, mercury lamps need to be kept within a specific temperature range to work best and thus need to be thermally insulated. For these reasons mercury and excimer lamps are surrounded by a protective sleeve, frequently in form of a tube of quartz.

[0016] 10 Excimer lamps require two electrodes, between which high voltage and high frequency AC power is applied. The high voltage is connected to an insulated inner electrode, which generally is surrounded by an inner transparent quartz sleeve, so as to not expose it to the excimer gas and thereby reduce corrosion of the inner electrode. The excimer gas is contained within a volume between the inner transparent quartz sleeve and an outer transparent quartz sleeve. An outer electrode, placed directly on the outside surface of the outer quartz sleeve, for example, in form of a mesh, a net or a wire spiral, is connected to low voltage or to ground, with such connection being generally achieved by drawing a wire from this outer electrode through the reactor body, thus requiring a rather complicated mechanical design that assures both, watertight sealing and electrical insulation.

[0017] These presently used photooxidation reactors for water purification systems providing the user with water of high purity have several problems. For both, mercury and excimer lamps, the wavelength necessary to photo-oxidize organic contaminants is very short and

[0018] 25 thus capable of degrading materials used in the construction of the photooxidation reactor. The protective quartz sleeves are essential to electrically insulate the lamp from the water and to also contain the excimer gas, but even the best quartz is not fully "transparent". Furthermore, UV radiation at the indicated wavelengths even degrades quartz.

[0019] With air as filling gas a further problem arises in that the emitted UV radiation leads to the formation of ozone, which is toxic to humans and in turn strongly absorbs radiation of wavelengths of less than 200 nm. Hence, for air as filling gas it will need to be ensured that the generated ozone cannot escape and cause harm to humans. Furthermore, ozone¬

[0020] 35 resistant materials would have to be used in construction. The volume between the lamp and the quartz sleeve is therefore ideally under vacuum or filled with a gas inert under these conditions, such as a noble gas, for example, xenon. However, it still remains a P24-250

[0021] - 3 - challenge to ensure gas tightness over the full range of temperature and the resulting filling gas pressures, particularly seeing that none of the known elastomer sealants is capable of withstanding the direct radiation at such wavelengths and the exposure to ozone.

[0022] 5

[0023] Seeing that the use of a quartz sleeve has a number of significant drawbacks, notably in respect to the yield of radiation as well as causing additional complexity in construction and operation, there is a need to provide for a photooxidation reactor that does not have these disadvantages, is safe to operate, and easier to assemble, such photooxidation

[0024] 10 reactor being particularly suitable for treating water having low conductivity.

[0025] A recent example of a flow-through photooxidation reactor is disclosed, for example, in US 6,633,109 B2. Further examples of photooxidation reactors can be found in US 2012 / 237409 Al, in US 2020 / 048111 Al, or in US 2024 / 334561 Al.

[0026] Summary

[0027] The present inventors have now surprisingly found that the above objectives can be attained either singly or in any combination by the flow-through photooxidation reactor and the method of the present application.

[0028] The present application therefore provides for a flow-through photooxidation reactor comprising

[0029] (i) a reactor vessel (2) comprising an inlet (3) and an outlet (4) for liquid (10a) to be

[0030] 25 processed, wherein the liquid to be processed may be, preferably is, water having a conductivity of at most 20 pS / cm, said reactor vessel defining an inner volume (10) through which the liquid (10a) flows in operation from the inlet (3) to the outlet (4), and

[0031] (ii) an excimer UV lamp (5) in the form of a bulb (8) having a transparent outer surface, wherein the transparent outer surface of the bulb (8) is a quartz sleeve (8a), comprising an inner electrode (6) and an excimer gas (7) surrounding and being in direct contact with the inner electrode (6), said excimer UV lamp (5) being arranged in the inner volume (10) of the reactor vessel (2) such that the transparent outer surface of the bulb (8), i.e. the quartz sleeve (8a), is at least partially exposed to the

[0032] 35 inner volume (10) of the reactor vessel (2) so that liquid (10a) can directly contact the outer surface of the bulb (8), i.e. the quartz sleeve (8a), P24-250

[0033] - 4 - wherein the reactor vessel (2) is at least partly made of an electrically conductive material such that the electrically conductive material is exposed to the liquid (10a) comprised in use in the reactor vessel (2) on at least part of the inner surface of reactor vessel (2), and the electrically conductive material of the reactor vessel (2) is connected to a low voltage

[0034] 5 or a ground terminal of an inverter circuit for driving an internal electrode (6) of the excimer UV lamp (5), or wherein - for the reactor vessel (2) being made of an electrically non-conductive material - the reactor vessel (2) comprises an electrode adjacent the inner surface of the reactor vessel and connected to a low voltage or a ground terminal of an inverter circuit for driving an internal electrode (6) of the excimer lamp (5).

[0035] 10

[0036] Thus, the present application also provides for the use of such a flow-through photooxidation reactor in a laboratory ultrapure water production system to treat water having a conductivity of at most 20 pS / cm with UV radiation.

[0037] Furthermore, the present application provides for a method of treating water, the method comprising the steps of

[0038] (a) providing water having a conductivity of at most 20 pS / cm to a flow-through photooxidation reactor (1) as defined in any of claims 1 to 12;

[0039] (b) treating in the photooxidation reactor (1) said water by irradiating with UV light.

[0040] Preferred features are indicated in the dependent claims.

[0041] Brief description of the drawings

[0042] 25 The present photooxidation reactor will in the following be described in detail making reference to the following exemplary, non-limiting, schematic drawings:

[0043] Figure 1 shows an exemplary, non-limiting, schematic illustration of a cross-section of the photooxidation reactor as defined in the present application in longitudinal direction through the center of the photooxidation reactor.

[0044] Figure 2 shows an exemplary, non-limiting, schematic illustration of a cross-section of the photooxidation reactor of Figure 1 along line A-A'. P24-250

[0045] - 5 -

[0046] Detailed description

[0047] In general terms, the present flow-through photooxidation reactor comprises a reactor vessel and an excimer UV lamp. The reactor vessel defines an inner volume, wherein the

[0048] 5 excimer UV lamp and - when the flow-through photooxidation reactor is in use or operation - the liquid to be treated, preferably water as defined herein, are comprised.

[0049] The liquid to be treated in the present flow-through photooxidation reactor is water having a conductivity of at most 20 pS / cm, for example, of at most 15 pS / cm, or of at most

[0050] 10 10 pS / cm, or of at most 9 pS / cm, or of at most 8 pS / cm, or of at most 7 pS / cm, or of at most 6 pS / cm, or of at most 5 pS / cm, or of at most 4 pS / cm, or of at most 3 pS / cm, or of at most 2 pS / cm, or of at most 1 pS / cm, or of at most 0.5 pS / cm, or of at most 0.4 pS / cm, or of at most 0.3 pS / cm, or of at most 0.2 pS / cm, or of at most 0.1 pS / cm.

[0051] The excimer UV lamp is comprised / arranged in the inner volume of the reactor vessel such that a transparent outer surface of a bulb of the excimer lamp is at least partially exposed to the inner volume of the reactor vessel. This allows said liquid to directly contact the transparent outer surface of the bulb of the excimer UV lamp.

[0052] Preferably, the reactor vessel and the excimer UV lamp both have a cylindrical shape and are in a concentric arrangement.

[0053] The present excimer UV lamp preferably is in form of a bulb ("light bulb") comprising an inner electrode, an excimer gas, and a transparent outer surface. Said bulb preferably has

[0054] 25 an elongated cylindrical / tubular configuration.

[0055] Though the present excimer UV lamp may be supported at both its ends, for ease of implementation, the excimer UV lamp is advantageously supported in the inner volume of the reactor vessel at only one axial end of the bulb. This may either be the end in proximity of the inlet or the end in proximity of the outlet of the reactor vessel.

[0056] Generally, the transparent outer surface of the bulb of the excimer lamp is a quartz sleeve, preferably a cylindrical quartz sleeve, sealed at both ends towards the environment. Sealing may, for example, be effected using plugs or adapters made of polycarbonate,

[0057] 35 glass or a ceramic material. These plugs or adapters may be attached to the quartz sleeve with epoxy glue. Alternatively, for plugs or adapters made of glass, the cylindrical quartz sleeve may be closed off at both ends with plugs of glass by depositing molten glass in P24-250

[0058] - 6 - form of a plug or by using molten glass as the "glue" for attaching a pre-fabricated glass plug in place, and in both cases then letting the molten glass cool. Sealing between the excimer lamp bulb and the reactor vessel is generally effected with O-ring seals.

[0059] 5 Advantageously, the excimer lamp comprises an inner electrode, an excimer gas, and a cylindrical quartz sleeve (as transparent outer surface of the bulb of the excimer lamp), with the inner electrode and the excimer gas comprised within the cylindrical quartz sleeve, with the inner electrode being surrounded by / in direct contact with the excimer gas.

[0060] 10

[0061] Thus, in contrast to conventional excimer UV lamps, wherein the inner electrode is surrounded by an inner quartz sleeve, and the excimer gas is comprised between such inner quartz sleeve and an outer quartz sleeve, the present excimer UV lamp lacks such inner quartz sleeve enclosing and electrically insulating the inner electrode by itself as well as lacking an outer / external electrode adjacent the second (outer) quartz sleeve.

[0062] For reasons of avoiding any unnecessary corrosion due to the inner electrode being in direct contact with the excimer gas, the excimer gas used in the present excimer UV lamp is advantageously a noble gas or a noble gas compound. Exemplary noble gases that may be used are selected from the group consisting of argon, neon, krypton, and xenon. As example of a noble gas compound mention may be made of krypton chloride (KrCI), the emitted radiation then having a main wavelength of 222 nm.

[0063] In the present application, the excimer UV lamp preferably emits radiation with a main

[0064] 25 wavelength of 172 nm. Thus, xenon is the preferred excimer gas.

[0065] Generally, the reactor vessel is of cylindrical shape, i.e. has a circular cross-section and a certain length. Diameter and length of such cylinder depend upon the specific use, particularly on the targeted flow rate of the liquid passing through the photooxidation reactor. For example, for use in the production of a liquid of high purity, such as ultrapure water, with a flow rate of up to 2 l / min, its diameter is generally of a few centimeters and its length, for example, of from 10 cm to 20 cm. The person skilled in the art can easily adapt these dimensions to the desired flow rate without any further inventive activity.

[0066] 35 The reactor vessel also comprises an inlet and an outlet for the liquid to be treated. So as to ensure that the reactor vessel is completely filled with the liquid to be treated, the photooxidation reactor and by consequence the reactor vessel are generally placed such P24-250

[0067] - 7 - that the flow of the liquid to be treated is upwards. In other words, the longitudinal axis of the reactor vessel preferably is essentially vertical, with the liquid flow from inlet to outlet being upwards. Such arrangement also ensures sufficient residence time of the liquid to be treated inside the photooxidation reactor by allowing to control the flow rate

[0068] 5 of the liquid inside the reactor.

[0069] The present reactor vessel either is at least partly made of an electrically conductive material such that the electrically conductive material is exposed to the liquid comprised in use in the reactor vessel on at least part of the inner surface of reactor vessel, or - for

[0070] 10 the reactor vessel being made of an electrically non-conductive material - the reactor vessel comprises an electrode, for example, a mesh, a net or a wire (for example, a spiral wire) electrode, adjacent the inner surface of the reactor vessel. For ease of production and maintenance it is, however, advantageous that the reactor vessel is at least partly made of an electrically conductive material as described above.

[0071] As electrically conductive material stainless steel, such as stainless steel 316, may be used.

[0072] Optionally, the present flow-through photooxidation reactor may further comprise baffle plates arranged in the inner volume of the reactor vessel to create a flow directional component towards the exposed surface of the bulb in the liquid flowing along a flow path from the inlet to the outlet, and arranged in the inner volume of the reactor vessel so as to be spaced apart from an outer peripheral surface of the bulb. The baffle plates are electrically insulating so as to avoid localized discharges. Preferably such baffle plates are axially spaced apart from each other. Alternatively, such baffle plates are axially spaced

[0073] 25 apart from each other and connected to each other to form a self-supporting structure.

[0074] The present photooxidation reactor will in the following be described in more detail with reference to the attached figures.

[0075] Figure 1 shows an exemplary, schematic, non-limiting illustration of the flow-through photooxidation reactor (1) as defined herein, the flow-through photooxidation reactor (1) comprising reactor vessel (2) and excimer UV lamp (5), with the excimer lamp (5) being comprised in the inner volume (10) of the reactor vessel (2). Excimer UV lamp (5) comprises within bulb (8) the inner electrode (6), the excimer gas (7), and quartz sleeve

[0076] 35 (8a) sealed at top and bottom with plugs or adapters (9a, 9b). As shown, when in use, i.e. when inner volume (10) of reactor vessel (2) is filled with liquid to be treated (10a), excimer UV lamp (5) is directly immersed in the liquid (10a), i.e. liquid (10a) directly P24-250

[0077] - 8 - touches the outer surface of quartz sleeve (8a) of bulb (8). Inner electrode (6) and the inner surface of the electrically conductive reactor vessel (2) are electrically, e.g. through wires (12) and (13), connected to an inverter circuit (11) for driving inner electrode (6) of the excimer lamp (5).

[0078] 5

[0079] Figure 2 shows a cross-section of the photooxidation reactor of Figure 1 along line A-A', with inner electrode (6) being surrounded by excimer gas (7), which in turn is contained within bulb (8) of excimer lamp (5) by quartz sleeve (8a), with the reactor vessel (2) and the excimer UV lamp (5) being concentrically arranged.

[0080] 10

[0081] The present inventors have surprisingly found that the flow-through photooxidation reactor as defined herein allows being run with essentially non-conductive water as defined herein.

[0082] Thus, the flow-through photooxidation reactor as defined herein may advantageously be used in a laboratory ultrapure water purification system to treat water having a very low conductivity as defined herein with UV radiation. Therein the present flow-through photooxidation reactor offers the particular advantage that it may be placed - in direction of the flow of water through the water purification system - after ion exchange steps, thereby allowing to remove any organic contaminants that the ion exchange resins may have introduced into the flow of to-be-purified water.

[0083] Consequently, the present application also provides for a method of treating water, the method comprising the steps of (a) providing essentially non-conductive water to a flow-

[0084] 25 through photooxidation reactor as defined herein, and (b) treating in the photooxidation reactor said water by irradiation with UV light.

[0085] In addition to the already indicated advantages of, for example, being easier to assemble, the present flow-through photooxidation reactor offers reduced energy consumption while maintaining performance, or alternatively improved performance (e.g. quicker decomposition of organic contaminants) while maintaining energy consumption. Furthermore, the present flow-through photooxidation reactor is safer to run because when empty, i.e. no water to be treated present in the reactor, the excimer UV lamp has been found to simply not light up. This avoids a "burn-through" of the lamp due to

[0086] 35 accidentally turning on the lamp. P24-250

[0087] - 9 -

[0088] Listing of the reference numerals

[0089] 1 Flow-through photooxidation reactor

[0090] 2 Reactor vessel

[0091] 3 Inlet

[0092] 4 Outlet

[0093] 5 Excimer UV lamp

[0094] 6 Inner electrode

[0095] 7 Excimer gas

[0096] 10 8 Excimer UV lamp bulb ("bulb")

[0097] 8a Quartz sleeve

[0098] 9a, 9b Plugs

[0099] 10 Inner volume of the reactor vessel

[0100] 10a Liquid to be treated

[0101] 11 Inverter circuit

[0102] 12,13 Wires

Claims

P24-250- 10 -Claims1. A flow-through photooxidation reactor (1), comprising5 (1) a reactor vessel (2) comprising an inlet (3) and an outlet (4) for liquid (10a) to be processed, wherein the liquid (10a) to be processed may be water having a conductivity of at most 20 pS / cm, said reactor vessel (2) defining an inner volume (10) through which the liquid (10a) flows in operation from the inlet (3) to the outlet (4), and10(ii) an excimer UV lamp (5) in the form of a bulb (8) having a transparent outer surface, wherein the transparent outer surface of the bulb (8) is a quartz sleeve (8a), comprising an inner electrode (6) and an excimer gas (7) surrounding and being in direct contact with the inner electrode (6), said excimer UV lamp (5) being arranged in the inner volume (10) of the reactor vessel (2) such that the quartz sleeve (8a) is at least partially exposed to the inner volume (10) of the reactor vessel (2) so that liquid (10a) can directly contact the quartz sleeve (8a), wherein the reactor vessel (2) is at least partly made of an electrically conductive material such that the electrically conductive material is exposed to the liquid (10a) comprised in use in the reactor vessel (2) on at least part of the inner surface of reactor vessel (2), and the electrically conductive material of the reactor vessel (2) is connected to a low voltage or a ground terminal of an inverter circuit for driving25 the internal electrode (6) of the excimer UV lamp (5), or wherein - for the reactor vessel (2) being made of an electrically non-conductive material - the reactor vessel(2) comprises an electrode adjacent the inner surface of the reactor vessel and connected to a low voltage or a ground terminal of an inverter circuit for driving an internal electrode (6) of the excimer UV lamp (5).

2. The flow-through photooxidation reactor (1) according to claim 1, wherein the inner volume (10) comprises the liquid (10a) to be processed, when the flow-through photooxidation reactor is in operation.35 3. The flow-through photooxidation reactor (1) according to claim 1 or claim 2, wherein the bulb (8) of the excimer UV lamp (5) has an elongated cyli ndrica l / tubula r configurationP24-250- 11 -4. The flow-through photooxidation reactor (1) according to any one of claims 1 to 3, wherein the excimer UV lamp (5) is supported in the inner volume of the reactor vessel (2) at only one axial end of the bulb (8).

55. The flow-through photooxidation reactor (1) according to any one of claims 1 to 4, wherein the transparent outer surface of the bulb (8) of the excimer UV lamp (5) is a quartz sleeve, preferably a cylindrical quartz sleeve sealed at both ends towards the environment.

106. The flow-through photooxidation reactor (1) according to any one of claims 1 to 5, wherein the excimer UV lamp (5) is configured to emit radiation with a main wavelength of 172 nm.

7. The flow-through photooxidation reactor (1) according to any one of claims 1 to 6, wherein the excimer UV lamp (5) is configured without an external electrode.

8. The flow-through photooxidation reactor (1) according to any one of claims 1 to 7, wherein the reactor vessel (2) and the excimer UV lamp (5) both have a cylindrical shape and are arranged concentrically.

9. The flow-through photooxidation reactor (1) according to any one of claims 1 to 8, further comprising baffle plates arranged in the inner volume (10) of the reactor vessel (2) to create a flow directional component towards the exposed surface of25 the bulb (8) in the liquid (10a) flowing along a flow path from the inlet (3) to the outlet (4).

10. The flow-through photooxidation reactor (1) according to claim 9, wherein the baffle plates are axially spaced from each other and preferably connected to each other to form a self-supporting structure.

11. The flow-through photooxidation reactor (1) according to any one of claims 1 to 10, wherein the reactor vessel (2) is a least partly made of an electrically conductive material, further comprising a spiral or a net or a mesh made from an electrically35 conductive wire material, the wire electrically conductively connected with the electrically conductive material of the reactor vessel and arranged in the inner volume so as to be spaced apart from an outer peripheral surface of the bulb.P24-250- 12 -12. The flow-through photooxidation reactor (1) according to any one of claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 15 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 15 to 11, wherein the liquid (10a) is water having a conductivity of at most 10 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 8 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 110 to 11, wherein the liquid (10a) is water having a conductivity of at most 7 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 6 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 5 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 4 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 3 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 2 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 1 pS / cm, or the flow-through photooxidation reactor according to any one of the claims 1 to 11, wherein the liquid (10a) is water having a conductivity of at most 0.5 pS / cm.2513. Use of a flow-through photooxidation reactor (1) as defined in any one of claims 1 to 12 in a laboratory ultrapure water production system to treat water having a conductivity of at most 20 pS / cm with UV radiation.

14. Method of treating water, the method comprising the steps of(a) providing water having a conductivity of at most 20 pS / cm to a flow-through photooxidation reactor (1) as defined in any of claims 1 to 12;(b) treating in the photooxidation reactor (1) said water by irradiating with UV light.

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