WO2007076579A1

WO2007076579A1 - Electro-chemical reactor

Info

Publication number: WO2007076579A1
Application number: PCT/AU2006/002008
Authority: WO
Inventors: Keith Laing; Peter Lansell
Original assignee: Cerezo Holdings Pty Ltd
Priority date: 2006-01-03
Filing date: 2006-12-21
Publication date: 2007-07-12

Abstract

The present invention provides a method of treating matter where said matter: (a) is a fluid or (b) is combined with a fluid; said method comprising the steps of: (i) subjecting at least part of said matter to shear; (ii) inducing cavitation in at least part of said fluid; and (iii) passing a current through (a) or (b). The invention further provides an apparatus for treating matter in accordance with the method of the present invention.

Description

"Electro-chemical reactor"

Cross-Reference to Related Applications

The present application claims priority from Australian Provisional Patent Application No 2006900577, Australian Provisional Patent Application No 2006906630 filed on 3 January 2006, 27 November 2006, the contents of which are incorporated herein by reference.

Field of the Invention:

The present invention is directed to an apparatus and method for achieving a chemical and/or physical change in matter, for example, in the conversion of minerals into preferred chemical feedstock and the breakdown of ores into their constituent elements.

Background of the Invention: The breakdown of various materials into their constituent parts has vast potential environmental and economic benefits and may find application in processes such as waste treatment and the conversion of low valued material into high valued chemical feedstock and products. For instance, asbestos, a once commonly used component in surfacing material in walls and ceilings, is now recognised as presenting a health risk as inhalation of asbestos fibres poses the risk of a variety of lung diseases including asbestosis, mesothelioma and broncogenic carcinoma. Due to its hazardous nature, the breakdown and/or disposal of asbestos is problematic, and special procedures are required to be followed before this material can be disposed to landfill which is undesirable from an economic and environmental viewpoint. One method of achieving material breakdown is by the use of ultrasound (or sonication). In this method, acoustic (or ultrasonic) energy is applied to a liquid medium causing the formation of small bubbles or cavities (cavitation) which subsequently expand and explosively collapse. The formation, expansion and ultimate collapse of the bubbles, known as cavitation, is accompanied by the release of intense vibrational energy.

International Patent Application No. WO 98/45418 describes an improved method for the enzymatic hydrolysis of lignocellulose comprising subjecting an aqueous mixture containing lignocellulose to ultrasound and contacting the mixture with a cellulase under conditions sufficient for hydrolysis. Another process using ultrasound is described in US 5,859,236 in which ultrasound is used as an improved means of converting the cellulosic fraction to microcrystalline cellulose. The use of ultrasound is also described in EP 0 952116 in which a process is disclosed comprising slurrying sludge to be treated and applying ultrasonic radiation to the slurry to decompose dioxins contained in the sludge. In all of these processes, ultrasonic oscillations are produced by the use of basic ultrasonic devices. The use of such devices however makes it difficult to achieve efficient and cost effective large-scale sonication processes. In an effort to address this problem, the use of hydrodynamics has been investigated as a means of initiating sonochemical reactions. An example is described in WO 98/50146, in which a method and apparatus of conducting sonochemical reactions and processes using large-scale liquid medium volumes is disclosed. This is achieved by flowing liquid medium through a channel that contains one or more elements that produce local constriction of the liquid flow. Downstream of these local constriction zones, cavitation bubbles are created and subsequently collapsed in an elevated pressure zone thereby initiating sonochemical reactions and processes. During the collapse of the cavitation bubbles very high localised pressures and temperatures are achieved which assist in the initiation of various chemical and or physical reactions. Despite this, many materials remain recalcitrant to breakdown upon the subjection to ultrasound, and indeed, methods of achieving more efficient material breakdown are desirable.

Summary of the Invention:

In a first aspect, the present invention provides a method of treating matter where said matter:

(a) is a fluid or (b) is combined with a fluid; said method comprising the steps of:

(i) subjecting at least part of said matter to shear; (ii) inducing cavitation in at least part of said fluid; and (iii) passing a current through (a) or (b). Preferably, steps (i), (ii) and (iii) are conducted concurrently, however, steps (ii) and (iii) may be conducted intermittently during step (i).

The matter to be treated may be a single substance or a mixture of two or more substances. The method of the invention may be a batch process or a continuous process. The fluid is preferably aqueous in nature. Where necessary, in addition to the aqueous fluid, an electrolyte may be added to said matter. The electrolyte may be acidic or alkaline in nature. Preferably the electrolyte is a hydroxide. Preferably the hydroxide is sodium hydroxide, however a hydroxide having a another counter ion may be adopted. Preferably the hydroxide is added to initiate current flow through at least part of said fluid. Preferably also, the hydroxide is added in an amount sufficient to initiate conductivity in the matter to be treated. The fluid in combination with the matter to be treated may be in the form of, for example, a slurry, an emulsion, a dispersion or a suspension or the like.

The electric current may be alternating current (AC) or direct current (DC). The current may be selected to have a desirable voltage, frequency and/or waveform. The voltage may be about IV to about 50V. The frequency may be up to about 50 MHz. The current may be of any waveform such as, for example, a square or sinusoidal waveform. A square waveform is preferred.. When the electric current is passed through the fluid, the fluid acts as an electrolytic connection within which free hydroxyl ions are created. It is believed that this has the effect of accelerating the breakdown of the matter to be treated.

In a second aspect, the present invention provides an apparatus for treating matter where said matter:

(a) is a fluid, or

(b) is combined with a fluid; said apparatus comprising: a vessel for containment of said matter; means for inducing cavitation in at least part of the fluid; means for generating shear; and at least two electrodes adapted to be held at a respective first and second predetermined voltage potential and located so as to allow a current to pass through at least one region in which at least part of said matter to be treated is located.

Preferably, the apparatus is configured to allow the passage of an electric current through localised zones of cavitation and high shear. It appears that when material is subjected to tension or shear and an appropriate electric charge is applied to the material, the chemical bonds within the material are temporarily or permanently disrupted. The combined shear and suitable electric charge, coupled with cavitation significantly reduces the energy needed for comminution.

Preferably, cavitation is induced by high speed rotation. Cavitation may also be induced by other means, for example, an external ultrasound device. In one embodiment, the vessel acts as an electrode. The vessel may also be lined on the inner surface with a material that acts as the first electrode and the means for inducing cavitation acts as the second electrode.

The vessel may be of any desired configuration capable of retaining matter as the process is conducted either batchwise or continuously. For example, the vessel may be cylindrical, spherical or tubular in shape. Preferably the vessel is of a cylindrical configuration.

The means for inducing cavitation may assume any one of a variety of configurations such as, for example, rotating disk(s) or impeller(s), baffle(s) or constriction zone(s), or any two or more of these configurations in combination. Such disks, impellers etc. may have smooth or rough surfaces. Such disks or impellers may have a wear resistant coating, or be fabricated out of wear resistant material, at regions in which high cavitation occurs. Such wear resistant materials or coatings may be, for example, diamond, tungsten carbide, or ceramic or the like. Preferably, the means of inducing cavitation is a rotating disk. The disk may have a substantially smooth circular periphery or the periphery of the disk may include at least one disconformity at which localised regions of cavitation are induced. The disk may be coated, or fabricated from, a wear resistant material at and/or about these regions of disconformity. The rotating disk may be welded to a substantially vertical shaft. The rotating disk may be situated within and near the base of the vessel and rotates independently of the vessel. The rotating disk may be positioned in a substantially horizontal orientation (i.e. about 90 degrees to the axis of the shaft) or may be inclined at less than about 90 degrees, such as, for example, 85 degrees to the axis of the shaft. Preferably, however, the rotating disk positioned in a substantially horizontal orientation. The vessel and disk may rotate in the same direction or in opposing directions, however the vessel may be stationary. The mode of operation of the vessel and/or disk depends on the particle size and/or density of the matter to be treated. The vessel and/or rotating disk may be made of a material of a suitable electrical conductivity. Suitable electrical conductivities range from 0.05 to 10 ohms/m, however, preferably, the material has a conductivity of less than about 1 ohms/m. Alternatively, the vessel may be lined with a material of a suitable electrical conductivity able to be held at a predetermined voltage potential.

The disk is preferably rotated at a relatively high velocity relative to the vessel and is such that a peripheral velocity of the matter is in excess of about 200 m/s. Under these conditions, the matter to be treated is subjected to mechanical shear forces and cavitation and is broken down into extremely fine material very quickly and with a much lower energy input compared to conventional comminution methods known in the art. The method and apparatus of the present invention may be operated at any suitable temperature or pressure. The method and apparatus may be operated at ambient or elevated pressure.. For example, the vessel may be operated at about atmospheric pressure and about 8O⁰C.

By the term "physical change", we mean that the matter to be treated undergoes a transformation in size, density, viscosity, and/or any other physical characteristic known to those skilled in the art, by the treatment method according to the present invention. By the term "chemical change", we mean that the matter undergoes a transformation in chemical bonding so at to produce a compound, element or substance having different physical and/or chemical characteristics following treatment.

The method and apparatus of the present invention may be used to achieve the physical (size) reduction of matter, initiate and/or accelerate chemical reaction(s) within matter. Examples of applications involving "physical reduction" include the manufacture of printing inks such as ink jet ink and in toner production as these products require very finely dispersed material so as to achieve a high printing quality. Other physical applications include the conversion of the structural nature of compounds, for example: the fibre composition of asbestos may be broken down into its constituent parts forming new structures of benign properties. The process may also be used to break down ore and extract various components sequentially. It can also be used in the manufacture of pharmaceuticals to produce finely divided or dispersed materials. Such finely divided pharmaceuticals can be readily absorbed through the skin or inhaled. Finely divided material can be readily mixed through cream formulations. Examples of applications involving chemical transformation include, but are not limited to, the breakdown of toxic hydrocarbons into benign species; the production of alcohol from carbonaceous matter; the cracking of hydrocarbons to lighter fractions; production of glasses and cement; processing of sewage and household waste; and in the complexing or extraction of heavy metals from ores or contaminated material. The process may also be used in the production of various hydrocarbons from coal and also in the recovery of metals from metal oxides, or in the conversion of asbestos fibres into benign species. The process may also be used for industrial processes involving nuclear fission and fusion and the reclamation of radioactive waste. This is facilitated by the ability of the device to be readily scaled-up to industrial proportions. . The chemical effects of high intensity ultrasound that arises from acoustic cavitation through the formation, growth and explosive collapse of bubbles in a liquid, when coupled with electro-facilitation and a shear force, are catalysed at a many-fold rate. This electro-chemical combination has a great cost-effective potential in many industrial processes.

The apparatus of the present invention is sometimes referred to by the inventors as the "Nanokey ballmill".

Throughout this specification the word "comprise", or variations such as

"comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

The invention will now be further described by way of a number of embodiments with reference the following non-limiting figures and examples.

Brief Description of the Drawings: Figure 1 is a schematic representation of the apparatus in accordance with an embodiment of the invention.

Figure 2 is a plan and side view of the apparatus in accordance with an embodiment of the invention.

Figure 3 is a plan and side view of the reactor lid in accordance with an embodiment of the invention.

Figure 4 provides views of the shaft connecting assembly in accordance with an embodiment of the invention.

Figure 5 is a plan and side view of the rotating disk in accordance with an embodiment of the invention.

Detailed Description of the Invention:

Referring to Figure 1, an embodiment of the invention provides a stainless steel cylindrical vessel (1) (200 mm diameter, five litre capacity) and lid (2), fitted with slip rings to allow a voltage to be applied to the vessel when it rotates about its axis in the vertical plane. A mixing disc assembly consisting of 150 mm circular disk (3) welded to the shaft (5) at an angle of 85 degrees to the axis of the shaft, with slip rings to allow a voltage to be applied to the mixing disc when it rotates about its axis in the vertical plane. The interior wall of the vessel is lined with a liner (9) comprising an insulating layer of polyethylene with a further layer of steel. The polyethylene layer provides the protection of the internal vessel surfaces while the steel liner acts as the electrode. Referring to Figure 2, another embodiment of the invention provides a containment vessel (as depicted in Figure 2) having a Hd (as depicted in Figure 3), shaft assembly (as depicted in Figure 4) and rotating disk (as depicted in Figure 5). The containment vessel is cylindrical, open at one end and closed on the other. The open end is flanged to receive the lid, which is designed to retain a high speed freely rotating disk in the event a fracture occurs at the shaft connection. The closed end is a heavy plate section and, in addition, an I beam base can be bolted to the heavy plate section, to give the vessel added weight and stability. A liner is to be inserted into the vessel (see below).

The rotor consists of a flanged shaft and a disk. The rotor is connected to a suitable drive medium.

Vessel

The containment vessel (Figure 2) in this embodiment is made from 13 mm steel plate, rolled into a 1320 mm inside diameter configuration, and seam welded along a dimension for the full thickness of the metal, forming an open ended cylinder 581 mm long. The longitudinal seam weld may be ground to a smooth surface on the inside of the cylinder.

A 19 mm thick mild steel base plate, 1500 mm x 1500 mm, the centre point of which is located slightly off-centre from the axis of the cylinder, is fillet welded both sides at the base of the cylinder. 4 off 380 (nominal) mm x 190 mm x 10 mm I beam sections are welded into a square and bolted with fifteen 29 mm diameter bolts to the edges of the steel plate. Slots may be cut in the I beam section to allow access for forklift tynes. Sixteen 29 mm diameter bolts are used to lock the I beam square frame to the concrete floor. The flange at the top of the cylinder is to be a 19 mm thick annulus of outside diameter 1520 mm, inside diameter 1346 mm, (cut from the stock used for the rotor disk). It is to be fillet welded to the containment vessel on the bottom side of the flange and seam welded then ground back to a smooth finish on the top side. Twelve 19 mm holes are to be drilled at equally spaced intervals, (30° intervals), on a 1477 mm diameter centre line.

All welds may be prepared for full section penetration. Holes are drilled around the circumference of the vessel at 60° to hold the insulating bushes fixing the liners to the vessel.

The vessel with lid attached, (with the centre hole suitably sealed and an appropriate gasket between the vessel and the lid), may be used as a rotary moulding machine to fabricate a vessel liner as follows. Polyethylene granules may be placed into the vessel and suitable binding agents added to the internal metal surfaces. The unit may be adapted to a rotary moulding frame that has been used to produce other equipment, a heat source added, and an insulating skin of polyethylene attached to the internals of the vessel and lid. This activity provides the necessary electrical insulation protecting all of the internal surfaces.

There may be a steel liner 13 mm thick and 300 mm wide around the full circumference of the internal diameter polyethylene insulating skin. The mid-point of the width of the liner may be in the same plane as the rotating disk. The liner may be segmented (circumferentially) into three parts, each part being secured by four machine screws bolted from outside the vessel into a threaded locations machined on the liner parts. The segments are made by rolling a 1300 mm outside diameter cylinder 300 mm wide and making three cuts down the longitudinal axis 120 degrees apart. The machine screws will be electrically insulated from the vessel and the bolts connected to a common busbar. The vessel is to be maintained at earth potential.

Three sets of 4 holes spaced 200 mm apart on the vertical axis are drilled equally spaced around the periphery of the cylindrical liner and tapped for a 19 mm metric thread. Clearance holes, accommodating the insulating bushes and in line with the tapped holes in the segments, are drilled in the cylindrical section of the containment vessel to allow the fixing of bolts from outside the vessel.

Lid

The lid (Figure 3) for the containment vessel shown in Figure 2 is made from 13 mm steel plate. It may be attached to the containment vessel by twelve 19 mm bolts, equally spaced (15°) around a 1477 mm diameter centre line, matching the pre-drilled holes on the flange of the containment vessel.

The lid when closed covers the top of the containment vessel except for a circular area, (360 mm diameter), allowing access for the flanges of the shaft of the rotating disk. The lid is reinforced with twelve 50 mm x 10 mm x 473 mm radial strengthening and attachment webs from the outer circular web (1346 mm mean diameter), to the inner circular web (400 mm mean diameter). The circular webs are made from 50 mm x 10 mm rectangular flat rolled to suit the required diameter of the respective circles.

A gland seal is to be fitted inside the 400 mm inner circular web, sealing the vessel from the external environment at the machined finish on the outer diameter of the rotating shaft.

Shaft

The shaft (Figure 4) is 200 mm outside diameter, 170 mm inside diameter, and 740 mm long and fabricated from mild steel. Mild steel flanges, have annular dimensions of 356 mm outside diameter and 200 mm inside diameter. Eight 19 mm holes are to be drilled at equally spaced intervals on a 306 mm diameter centre line, ie. at 45° intervals. The flanges are to be welded to the shaft ensuring full penetration between the flanges and the shaft. The mild steel bosses, one male the other female at the exposed end, are pressed into the shaft and welded after preparation of the weld area by veeing to the depth of 19 mm.

Welds are full section from the face side of the flange with a supporting fillet weld on the shaft side. Faces of the flanges are to be machined parallel with one another and right-angled to the shaft axis. The shaft is dynamically balanced.

Rotating Disk

The rotating disk (Figure 5) is made from mild steel 19 mm thick with a tip diameter of 1270 mm, root diameter of 1120 mm, six teeth with a radial tooth profile of 740 mm stepped out from a locus circle of 358.6 mm diameter at the centre of the disk.

A 6 mm x 75 mm male spigot is to be centred on the disk and welded to the surface of the disk as the locating medium for the disk to the shaft. The disk is to be drilled to match the flange of the shaft, fitting and dynamically balanced.

Example 1:

Two kilograms of used asbestos pipe lagging (inclusive of paint, rust, water, mud and other impurities) was placed in the vessel (1) and water added to completely cover the asbestos fill. The mixing disk assembly was positioned in the vessel with the axis of the shaft (5) vertical and slightly off-centre to the vertical axis of the vessel, and the disk (3), (now immersed in the asbestos and water mix), in close proximity to the bottom of the vessel (1) but without touching the vessel (1). The positive terminal of the variable direct current power supply was connected to the slip rings on the vessel, the negative terminal to the slip rings on the shaft, 28 volts was applied to the circuit and a small current flow of less than 2 amperes was observed. The mixing disk (3) (powered by a 3 HP electric motor), was rotated at 12,500 revolutions per minute. The vessel was rotated in the same direction at 30 revolutions per minute. 50 grams of sodium hydroxide was added to the asbestos and water mix.

It was observed that the current draw on the equipment rose quickly to 40 amperes and because of the limitations of the direct current power supply that was used and an increasing conductivity on the slurry, (caused by an increasing pH in the fluid), the voltage was progressively reduced to maintain a 40 ampere current. After mixing for 10 minutes the contents of the bowl appeared as a very consistent creamy mix. The mix was allowed to stand for 3 hours and silicates precipitated out in several layers of varying solubility and particle size, leaving a clear nascent hydroxide (liquid) mix as a top layer.

It was observed that the process is remarkably efficient in terms of comminution energy. The apparatus successfully separated the components of asbestos into a variety of hydroxides and oxides. This had the effect of completely destroying the (medically harmful) fibre structure of the asbestos material, with the residue of elemental constituents (mainly silicates) taking up their conventional (benign) three-dimensional crystalline structures. The experiment also indicated that all the various species could be extracted from the original asbestos mix slurry, sequentially and preferentially, in order of their placement on the galvanic table. (Refer "Reference Data for Radio Engineers, Second Edition, page 414).

Example 2:

Another experiment was conducted using 1 part (by weight) of sodium hydroxide to 3 parts (by weight) of clean sand and mixing in the stainless steel reactor (1). Using similar voltages to that used in Example 1, it took 15 minutes to produce a clear honey coloured liquid containing no discernable particulate matter. Further testing demonstrated that the material appeared to exhibit exactly the same characteristics and perfoπnance as commercial sodium silicate solution. If calcium were to be used in preference to sodium then it is likely that a tri-calcium silicate solution (portland cement) could be manufactured. This would be a low temperature, environmentally friendly means of producing cement. The extraction of particular minerals from the solution is a function of its solubility (or the pH at which the mineral become a solute), ie., its chemical readiness to form a hydroxide. The constituents in the slurry, one at a time, are removed preferentially as they reach their soluble condition, ie., at an appropriate pH. The order that the minerals in the slurry become soluble is a function of the ranking of the particular mineral on the galvanic table. The continued production of hydroxyl ions in the reactor (from electrolysis, and a lesser extent from the cavitation activity around the disk) tends to progressively increase the pH of the slurry. However, if the pH is of such a value that allows a particular constituent of the mix to form a hydroxide, then the pH will remain constant until that entire constituent has been consumed to form the hydroxide, (this is so for the operating parameters of this experiment, where the pH is slowly increasing). When that constituent is entirely consumed, the pH starts to rise again until the next constituent becomes soluble in solution. This process can continue until nothing but insoluble constituents, if any, remain.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A method of treating matter where said matter:

(a) is a fluid or

(b) is combined with a fluid; said method comprising the steps of:

(i) subjecting at least part of said matter to shear;

(ii) inducing cavitation in at least part of said fluid; and

(iii) passing a current through (a) or (b).

2. A method according to claim 1 wherein steps (i), (ii) and (iii) are conducted concurrently.

3. A method according to claim 1 wherein steps (ii) and (iii) are conducted intermittently during step (i).

4. A method according to any one of the preceding claims wherein the fluid is an aqueous fluid.

5. A method according to any one of the preceding claims wherein an electrolyte is added to said matter.

6. A method according to claim 5 wherein the electrolyte the electrolyte is a hydroxide.

7. A method according to claim 5 or claim 6 wherein the electrolyte is sodium hydroxide.

8. A method according to any one of the preceding claims wherein the electric current has a voltage of about IV to about 50 V.

9. A method according to any one of the preceding claims wherein the current has a frequency up to about 50 MHz.

10. A method according to any one of the preceding claims wherein the current has a square waveform.

11. An apparatus for treating matter where said matter:

(a) is a fluid, or

12. An apparatus according to claim 11 wherein the means for inducing cavitation is selected from rotating disk(s), impeller(s), baffle(s) or constriction zone(s) or two or more of such means in combination.

13. An apparatus according to claim 11 wherein the means for inducing cavitation is an external ultrasound device.

14. An apparatus according to any one of claims 11 to 13 wherein the vessel and/or means for inducing cavitation are made from a material having an electrical conductivity of about 0.05 to about 10 ohms/m.

15. An apparatus according to claim 14 wherein the material has a conductivity of less than about 1 ohm/m.

16. An apparatus according to any one of claims 11 to 15 wherein the vessel is lined with a material having an electrical conductivity of about 0.05 to about 10 ohms/m.

17. An apparatus according to claim 16 wherein the material has a conductivity of less than about 1 ohm/m.

18. An apparatus according to claim 12 wherein when the means of inducing cavitation is a rotating disk, the disk is rotated at a velocity sufficient to achieve a peripheral velocity of the matter in excess of about 200 m/s.

19. Matter treated in accordance with the method of any one of claims 1 to 10.