PHOTOCATALYTIC PANEL REACTOR FOR THE ANAEROBIC PHOTOREFORMING OF WASTE AQUEOUS EFFLUENTS AND THE PRODUCTION OF HYDROGEN AS CO-PRODUCT

Abstract

The invention discloses a photocatalytic reactor for the anaerobic photoreforming waste aqueous effluents and the production of hydrogen, comprising a flat panel with a shallow container (4) and a top transparent window (6); a bed (5) of photocatalyst material with a photoactive semiconductor and at least one co-catalyst; a flow region (8) through which a waste aqueous effluent flows and enters into contact with the photocatalyst material in the bed (5) under irradiation; and a sealing gasket (9) which isolates the panel from ambient air.

Claims

1. Photocatalytic panel reactor for the anaerobic photoreforming of waste aqueous effluents and the production of hydrogen as co-product characterized in that it comprises: at least one flat panel comprising: a shallow container (4) and a top transparent window (6), said top window (6) being intended to face a source of light; a bed (5) composed of a photocatalyst material, comprising at least one photoactive semiconductor, immobilised therein, the bed being located on an irradiated surface of the flat panel; a flow region (8) located in the shallow container (4), said region being arranged so that a waste aqueous effluent flows through it and enters into close contact with the photocatalyst material immobilised in the bed (5); and a sealing gasket (9) disposed between the shallow container (4) and the top transparent window (6), intended to ensure the tightness of the panel and its isolation from ambient air; (i) gas outlet ports (3) provided in the container (4), said outlet ports being connected through tubes to at least one gas-tight storage tank; or, alternatively, (ii) a recirculation circuit provided with: a tank at least one external pump intended to make the aqueous effluent recirculate from the tank to the container (4) and then from the container (4) back to the tank; and a gas-liquid separation chamber, said gas-liquid separation chamber being connected through tubes to at least one gas-tight storage tank and comprised in an elevated part of the recirculation circuit, wherein the photocatalyst material also contains at least one co-catalyst in the form of particles deposited on the surface of the photoactive semiconductor, said co-catalyst comprising: metals; metal oxides, metal sulphides, metal phosphides and/or organometallic species; and combinations thereof.

2. Panel reactor according to claim 1, wherein the photoactive semiconductor is chosen among: Metal oxides; Mixed metal oxides; Metal sulphides; Metal halides; Metal phosphates; Organic semiconductors; Hybrid organic-inorganic semiconductors; and combinations thereof.

3. Panel reactor according to claim 1, wherein the top transparent window (6) is made from borosilicate glass, low-iron glass, quartz, and/or polycarbonate.

4. Panel reactor according to any previous claim 1, wherein the shallow container (4) comprises material of construction selected from the group consisting of: a metal selected between aluminium, stainless steel, brass, iron, and/or titanium; a plastic selected between resins, polyvinyl chloride, polyurethane, polypropylene and/or polyethylene; a ceramic material selected between alumina, clay, and/or stone; and combinations thereof.

5. Panel reactor according to claim 1, wherein the shallow container (4) is provided with at least one inlet port (1) and at least one outlet port (2) for the flow of the aqueous effluent.

6.-9. (canceled)

10. Panel reactor according to claim 1, also comprising a sun tracking system on which the at least one flat panel is mounted, the sun tracking system being intended to direct the top transparent window (6) of said panel along the azimuth.

11. Use of a photocatalytic panel reactor according to claim 1, for the treatment of waste aqueous effluents derived from food industry activities, pharmaceutical industries, cosmetic or personal care products industries, chemical or petrochemical industries, biorefineries or biofuel production plants, papermaking industries, farming or agricultural activities, or human sanitation activities.

12. Panel reactor according to claim 1, wherein the bed (5) is a layer having a thickness in the range of 1-100 micrometers.

13. Panel reactor according to claim 1, wherein the co-catalyst comprises Cu, Fe, Co, Ni, Zn, Sn, Cr, Pb, Bi, Ag, Au, Pd, Rh, Ru, Pt, Ir, or Cd.

14. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more metal oxides selected from the group consisting of TiO.sub.2, FeO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, CoO, Co.sub.2O.sub.3, Cr.sub.2O.sub.3, MnO, Mn.sub.2O.sub.3, MnO.sub.2, NiO, Ni.sub.2O.sub.3, Cu.sub.2O, CuO, ZnO, ZrO.sub.2, WO.sub.3, SnO, SnO.sub.2, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, In.sub.2O.sub.3, Bi.sub.2O.sub.3, Sb.sub.2O.sub.3, Ce.sub.2O.sub.3, CeO.sub.2, Ag.sub.2O, Ga.sub.2O.sub.3, CdO, Hg.sub.2O, HgO, PbO, PbO.sub.2, and PdO.

15. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more mixed metal oxides selected from the group consisting of AlTiO.sub.3, Al.sub.2TiO.sub.5, BaTiO.sub.3, CaTiO.sub.3, MgTiO.sub.3, SrTiO.sub.3, CoTiO.sub.3, FeTiO.sub.3, NiTiO.sub.3, CuTiO.sub.3, MnTiO.sub.3, ZnTiO.sub.3, KNbO.sub.3, NaNbO.sub.3, YFeO.sub.3, CuFe.sub.2O.sub.4, BiVO.sub.4, KTaO.sub.3, and NaTaO.sub.3.

16. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises perovskite.

17. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more metal sulphides selected from the group consisting of TiS.sub.2, FeS, Fe.sub.2S.sub.3, CoS, Co.sub.2S.sub.3, Cr.sub.2S.sub.3, MnS, MnS.sub.2, NiS, Cu.sub.2S, CuS, ZnS, CdS, ZrS.sub.2, WS.sub.2, WS.sub.3, SnS, SnS.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3, Sb.sub.2O.sub.3, Ce.sub.2S.sub.3, CeS.sub.2, Ag.sub.2S, Ga.sub.2S.sub.3, Hg.sub.2S, HgS, PbS, PbS.sub.2, and PdS.

18. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more metal halides selected from the group consisting of AgI, AgBr, AgCl, HgCl.sub.2, and Hg.sub.2Cl.sub.2.

19. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more metal phosphates selected from the group consisting of Cu.sub.3 (PO.sub.4).sub.2, Cu.sub.2 (OH) PO.sub.4, Ag.sub.3PO.sub.4, Fe.sub.3 (PO.sub.4).sub.2, Zn.sub.3 (PO.sub.4).sub.2, Ni.sub.3 (PO.sub.4).sub.2, FePO.sub.4, CePO.sub.4, BiPO.sub.4, and TiP.sub.2O.sub.7.

20. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more doped or undoped organic semiconductors selected from the group consisting of covalent organic frameworks, C.sub.3N.sub.4, polyacetylene, polythiophene, and polypyrrole.

21. Panel reactor according to claim 2, wherein the photoactive semiconductor comprises one or more hybrid organic-inorganic semiconductors selected from the group consisting of metal-organic frameworks.

Description

BRIEF DESCRIPTION OF THE ANNEXED DRAWING

[0075] A detailed description of various aspects, features, and embodiments of the subject matter described herein is provided with reference to the accompanying drawing, which is briefly described below. The drawing is illustrative and is not necessarily drawn to scale, with some components and features being exaggerated for clarity. The drawing illustrates various aspects and features of the present subject matter and may illustrate one possible embodiment or example of the present subject matter in whole or in part.

[0076] FIG. 1 is an exploded perspective view of an embodiment of the photocatalytic panel reactor according to the present invention.

EXPLANATION OF NUMERICAL REFERENCES

[0077] 1 inlet port; [0078] 2 outlet port; [0079] 3 gas outlet port; [0080] 4 shallow container; [0081] 5 photocatalyst bed; [0082] 6 top window; [0083] 7 window frame; [0084] 8 flow region; [0085] 9 sealing gasket; [0086] 10 protective gasket.

DETAILED DESCRIPTION OF THE INVENTION

[0087] FIG. 1 shows one possible embodiment of the photocatalytic panel reactor according to the present invention.

[0088] In this particular example of the invention, the reactor comprises one flat panel formed by a shallow rectangular container (4) and a top rectangular window (6) which is transparent and is intended to face towards a source of light.

[0089] The shallow container (4) has vertical walls provided with housing holes. In turn, the perimeter of the top window (6) has a window frame (7) with a plurality of through holes.

[0090] A sealing gasket (9) is interposed between the upper part of the walls of the shallow container (4) and the top window (6). In addition, in this particular embodiment of the invention a protective gasket (10) is also placed on top of the top window (6), the window frame (7) being placed sitting on top of such gasket (9b). Finally, screws are passed through the aligned holes of both the container (4) and the frame (7), and tightened with bolts to close the panel, leaving the flow region (8) between the upward surface of the container and the bottom side of the window (6). As the sealing gasket (9) and the protective gasket (10) are compressed during the tightening of the screws and bolts, the interior of the flow region (8) is sealed and, simultaneously, the top window (6) which in this particular embodiment is made of glass, is protected from possible stress and local overpressure, thus avoiding its cracking or blowing up.

[0091] A bed (5) composed of a photocatalyst material, comprising at least one photoactive semiconductor isin this particular case-disposed inside flow region (8) and immobilised therein.

[0092] The flow region (8) is in fluid communication with an inlet port (1) and an outlet port (2), in such a way that a waste aqueous effluent enters into the flow region (8) via the inlet port (1), flows through it contacting with the photocatalyst material immobilised in the bed (5). Finally, the aqueous effluent leaves the flow region (8) through outlet port (2).

[0093] In this embodiment of the invention, the panel reactor is also provided with a gas outlet port (3), through which the hydrogen produced by waste degradation reaction under anaerobic conditions leaves the panel.

EXPERIMENTAL EXAMPLES

[0094] In order to prove the feasibility of this invention, experimental examples of one possible embodiments of a panel reactor according to the present invention are herein described. These examples include the design and construction of the panel, the preparation of a photocatalyst and its deposition in the form of photocatalyst bed, and an experimental test for hydrogen production under natural sunlight.

Experimental Example 1

Panel Design and Construction.

[0095] A prototype panel has been fabricated according to the drawing containing the following parts: [0096] A rectangular shallow container (4) made in aluminium, its external dimensions being 200300 mm, and its height is 30 mm. The top side of the container has a 140240 mm rectangular cavity, and its depth is 20 mm. Moreover, a 5 mm step is made around the cavity on top side rim of the container, and a slight carved channel is also machined along the step to allow for the sealing gasket to sit on it. Three side orifices were made across the side of the container to serve as liquid inlet (1), liquid outlet (2) and gas outlet (3) ports. Holes for pass-through screws are made across the panel external sides, as illustrated in the drawing. [0097] A rectangular sealing rubber gasket (9) sitting on top of the step and along the channel of the container, as described above. [0098] A rectangular low iron borosilicate glass top window (6), 5 mm thick, whose dimensions are approximately 150250 mm, to sit on top of the sealing gasket (9). [0099] A protective rubber gasket (10) on top of the glass window (6). [0100] A rectangular window frame (7), 200300 mm external size, and 10 mm thick, on top of the protective gasket (10). Holes for pass-through screws are made through the frame, aligned to those of the panel, as illustrated in the drawing. [0101] Through the aforementioned holes, screws are inserted so that they protrude and can be tightened with bolts to close, secure, and tight-seal the panel.

Photocatalyst Preparation.

[0102] As typical photocatalyst, platinum on titanium dioxide was prepared as follows. Hexachloroplatinic acid hexahydrate (55.3 mg) was dissolved in water (50 mL). Titanium dioxide powder (Aeroxide P25 from Evonik, 2.01 g) was added and the suspension stirred for 2 h. Then, water was distilled off using a rotary evaporator, leaving a yellow powder which was then calcined under static air atmosphere by heating at 2 C. min.sup.1 from 30 to 400 C., then maintaining the sample at 400 C. for 2 h and allowed to cool down slowly. The resulting pale yellow solid was then activated by thermal treatment under dihydrogen (20 mL min.sup.1) diluted with argon (500 mL min.sup.1) by heating at approximately 10 C. min.sup.1 from 30 to 450 C., then maintaining the sample at 450 C. for 3 h. The resulting grey solid had an approximate platinum concentration of 1% by weight relative to TiO.sub.2, and will be hereinafter designated as Pt-1/TiO.sub.2.

Deposition of the Photocatalyst on the Panel.

[0103] The photocatalyst was deposited by a simple casting method on the cavity bottom in the shallow container (4) forming a bed (5). A suspension containing Pt-1/TiO.sub.2 (1.00 g) and deionized water (20 mL) was prepared and sonicated for 15 min to disperse the solid. The suspension was carefully deposited on the shallow container cavity bottom and allowed to dry out by evaporation of water under ambient air for several hours. A layer of Pt-1/TiO.sub.2 photocatalyst bed was uniformly distributed on the container inner surface.

Testing of the Photocatalytic Hydrogen Production Under Natural Sunlight.

[0104] The panel was tightly closed as indicated above. To test the photoreforming activity, the chosen aqueous feedstock was a mixture of glycerol and water (20:80 volume ratio). After filling the flow region with the glycerol/water mixture, most residual air bubbles were removed through the gas outlet port by turning the panel to allow the liquid to fill most headspace by gravity. Liquid inlet and outlet ports were closed, whereas the gas outlet port was connected through a silicone rubber tube to a pressure gauge and a sampling valve. Initial pressure was roughly atmospheric (1.0 bar). The panel was exposed to natural sunlight during 3 h (12:00 to 15:00, Central European Summer Time) on a slightly inclined (<10 angle) orientation facing the Sun, in a well irradiated, shade-free area in the Sescelades campus in Tarragona (approximate location: 41.133 N, 1.245 E), on the 30th of July 2021. After an initial period (<0.5 h), bubbles started to be formed on the photocatalyst bed (5). With increasing sunlight irradiation time, bubble formation became faster and more visible, eventually resulting in significant gas build-up. In parallel, the panel became slightly warm, and some additional bubbles appeared evenly within the liquid on the flow region. After sunlight exposure, the panel was taken indoors, allowed to cool down and settle. The final pressure was 1.6 bar. A gaseous sample (8 mL) was collected in a gastight syringe and injected in a gas chromatograph (Agilent 990 Micro GC System) allowing to identify and quantify hydrogen. The amount of evolved hydrogen calculated according to its concentration, based on previous equipment calibration and on the estimated headspace volume, was approximately 1.5 mL (normal conditions).

Experimental Example 2

Testing of the Photocatalytic Hydrogen Production from Juice Production Plant Wastewaters, Recirculated from an External Tank, Under Natural Sunlight.

[0105] An experiment was performed following a similar procedure to the one described with regard to experimental example 1, using a mixture of glycerol and water as a model feedstock, but in this case using wastewaters sourced from a local juice production plant.

[0106] The panel was loaded with a freshly activated Pt-1/TiO.sub.2 sample (1.0 g) which covered essentially the entire inner, upward-facing, surface of the shallow container (4) shown in FIG. 1. Likewise, the panel was tightly closed by means of sealing gaskets (elements 9 and 10 in FIG. 1). The inlet and outlet ports (elements 1 and 2 in FIG. 1) were connected to the waste aqueous effluent circuit by means of silicone rubber tubing. In particular, the effluent circuit consisted of a tank (1 L) connected to the inlet of a peristaltic pump, which flowed the waste aqueous effluent from said tank to the panel through inlet port 1 by means of silicone rubber tubing. The tank was further equipped with a gas-tight valve so that it could be used as a gas-liquid separator (see below). Conversely, the outlet port (2) was connected directly to the tank, enabling the recirculation of the waste aqueous effluent back to said tank.

[0107] The tank and the panel container were then filled with a sample of juice production wastewaters (total volume=1.5 L, physico-chemical parameters summarized in Table 1) by first filling the tank and then pumping the wastewaters from into the panel until the shallow container was completely full. Next, the gas port (3 in FIG. 1) was employed as a purging port by flowing ultrapure argon (99.9995%, ca. 20 mL min.sup.1) through the aqueous effluent inside the shallow panel container under continuous recirculation of the effluent by means of the peristaltic pump. In this way, argon flowed from the panel into the tank. By keeping the gas-tight valve in the tank open, argon displaced the air in the tank headspace. This purging operation was continued until the level of oxygen (remaining from atmospheric air initially in the tank) in the headspace was below 0.5% by volume.

[0108] Initial pressure was slightly above atmospheric (ca. 1.2 bar). The panel was exposed to natural sunlight during 3 h (12:00 to 15:00, Central European Summer Time) at an adjusted angle (35 angle) to attain a nearly perpendicular incidence of sun beams on the photocatalyst bed, in a well irradiated, shade-free area in the Sescelades campus in Tarragona (approximate location: 41.133 N, 1.245 E), on the 7th of April 2022. During the entire experiment, the waste aqueous effluent was continuously recirculated by means of the peristaltic pump, also carrying any gas bubbles formed through the effluent circuit into the tank headspace. The average sunlight irradiance, as measured using a calibrated pyranometer, was 0.87 KW m.sup.2. Bubbles started to be formed on the photocatalyst bed immediately, resulting in significant pressure build-up in the tank headspace. Samples were collected after every hour of sunlight irradiation experiment through the gas-tight valve on the tank headspace by using a gas-tight syringe, and injected in the gas chromatograph described above. The amounts of evolved hydrogen calculated according to their concentration, based on previous equipment calibration and on the estimated headspace volume, were as follows:

TABLE-US-00001 TABLE 1 time/ V(H.sub.2)/mL (at standard conditions, h i.e. 273.15K and 1.0 bar) 1 211 2 292 3 328

[0109] The present invention should not be taken to be limited to the embodiment herein described. Other arrangements may be carried out by those skilled in the art based on the present description. Accordingly, the scope of the invention is defined by the following claims.