WO2004033097A1

WO2004033097A1 - Method and apparatus for treating liquids

Info

Publication number: WO2004033097A1
Application number: PCT/FI2003/000753
Authority: WO
Inventors: Erkki Paatero; Ari KÄRKI; Joni Helenius; Janne Kauppi; Esa Paavola
Original assignee: Larox Oyj; Finex Oy
Priority date: 2002-10-11
Filing date: 2003-10-10
Publication date: 2004-04-22
Also published as: FI20021814A; AU2003268983A1; FI118630B; AU2003268983A8; FI20021814A0

Abstract

The invention relates to a method and apparatus for treating liquids, in particular by means of an apparatus based on the use of an ion-exchange resin. The invention is characterized by the steps of passing the liquid being treated into a vessel (1) and therein treating the liquid by way of passing the liquid into at least one horizontal filter element (4) containing a thin layer of an ion-exchange resin and further therethrough to the exterior side of the vessel (1).

Description

Method and apparatus for treating liquids

The present invention relates to a method according to the preamble of claim 1 for treating liquids, particularly using an apparatus based on an ion-exchange resin, and an apparatus according to the preamble of claim 6 suitable for implementing the method.

The most conventionally used type of ion-exchange apparatus is based on an ion-exchange column typically adapted into a vertically aligned, cylindrical pressure vessel. The column is generally operated in a half-filled state, that is, supporting an about 1 to 2 m thick bed of loosely packed spherical bead ion- exchange resin particles through which the liquid to be treated is passed. After leaving the resin bed, the treated liquid is removed via a discharge nozzle mounted at the bottom of the column.

An unfilled freeboard space must be left at the top of column, because the volume of the resin bed changes slightly during operation. The freeboard space is also necessary for the regeneration or flushing of the resin bed in an operation wherein a flushing liquid passed in the reverse direction fluffs the resin bed and allows cracked resin particles to be removed as an overflow.

The resin bed represents a flow resistance that requires pressurization of the liquid being treated in order to force it through the resin bed. The inlet pressure must be sufficiently high to attain the specified flow rate. On the other hand, an excessive inlet pressure may compact the resin bed thus increasing its flow resistance, whereby the maximum possible flow rate is further reduced.

In this type of column, the resin generally used is in the form of spherical bead particles, the typical particle size of the resin being in the range of 0.5 - 1.2 mm whereby smallest diameter may be about 0.3 mm. While the use of large- diameter resin particles facilitates a low specific flow resistance, it on the other hand necessitates the use of a thick resin bed to attain an efficient liquid purifying effect. A thick resin bed is also necessary to avoid flow channeling because, due to the strong volume expansion of the resin, the liquid being purified avoids uniform flow through the volume of the bed and rather tends to form flow channels, whereby the purifying effect of the filter is substantially reduced.

The purification efficiency of the above-described construction is not quite satisfactory if a liquid solution must be purified free from large organic molecules or colloidal inorganic compounds. This is because such molecules cannot enter the pores of spherical bead resin particles or the diffusion of molecules into the pores is slow! The prior-art construction is also inefficient when the incoming liquids contain a low concentration of substances to be removed.

In the art is also known an arrangement in which onto vertical elements of tubular cross section located in a pressure vessel is deposited by filtration a thin layer of finely pulverized ion-exchange resin. In this type of apparatus, the solution to be purified can be passed at a high flow rate through the resin bed without facing an excessive pressure drop. However, such a construction requires continuous liquid flow through the resin bed, because otherwise the particular resin layer falls off from the surface of the vertical elements as soon as the pressure imposed thereon is lost.

It is known in the art that in the filtration of fine particles, the filter cake develops channels via which a substantial portion of the filtrate passes through the cake in a nonpurified condition. The risk of channeling is particularly pronounced if the filter cake happens to become dry. As to ion-exchange resins, it must be noted that the resin particles shrink and swell during operation thus causing additional channeling and leaks about the bed edges.

One prior-art arrangement aiming to prevent channeling in the layer of particular resin in a vertical filter element is to apply mechanical compression on the layer of ion-exchange resin. A drawback of this approach is the excessively high and inhomogeneous density of the bed.

It is an object of the present invention to overcome the above-mentioned drawbacks and to provide a compact apparatus that is based on the use of small-diameter particular ion-exchange resins and is suited for processing large volumes of liquids. The apparatus allows the liquid flow to be stopped and restarted without the risk of the above-described channeling. The above object is attained by virtue of a method and apparatus in accordance with the present invention, the apparatus having its horizontal filter elements superposed in tiers in a pressurized solid-wall vessel. According to the invention, on top of the filter elements is formed a thin layer, about 10 - 100 mm, typically 10 - 40 mm thick, of finely pulverized particular ion-exchange resin having a particle size in the range of 1 - 300 μm, typically 10 - 300 μm, with an elastic flow distribution element placed thereon in order to prevent cracking and channeling of the resin layer.

The characterizing features of the arrangement in accordance with the invention are specified in the characterizing parts of appended claims.

In the following, the invention is described in more detail by making reference to the attached drawings in which

FIG. 1 shows a longitudinally sectioned view of an apparatus according to the invention;

FIG. 2 shows the construction of a filter element according to the invention;

FIG. 3 shows the filtration result of an aqueous solution containing a floatation agent;

FIG. 4 shows the ash content of the dry solids of a hexane-based process solution; and

FIG. 5 shows the ash composition of the above exemplifying test.

Referring to FIG. 1 , an embodiment of the apparatus according to the invention comprises a pressure vessel 1 wherein the liquid to be purified is passed into the top portion of the vessel via an inlet pipe 2. To the bottom portion of the vessel 1 is connected an outlet pipe 3 via which the liquid passed through filter elements 4 leaves the vessel 1 in a purified condition. The vessel 1 is also equipped with a flange, bayonet or the like type of joint 5 that facilitates opening the vessel for servicing, replacement of elements 4 or other purposes. On the bottom of vessel 1 is mounted a support pipe 6 allowing the filter elements 4 to be placed thereon so as to form a contiguous stack 7 starting from the vessel bottom. While proper dimensions of the filter elements 4 give the stack 7 sufficient structural stability during operation, the elements 4 may additionally be supported to the inner walls of vessel 1. Above the filter element stack 7 is placed a guide baffle 8 for securing uniform distribution of the incoming liquid flow to all of the filter elements 4.

In FIG. 2 is shown an exemplary embodiment of a compatible filter element. The center tube 9 of filter element 4 comprises an inner center tube portion 10 and an outer center tube portion 11 having such compatible dimensions that the filter elements 4 can be self-lockingiy placed above one another into a contiguous stack 7 wherein the bottom-end inner center tube portion 10 of one element fits into the top-end outer center tube portion 11 of the next element 4 below.

To the center tube 9 comprising the inner and outer center tube portions 10 and 11 is attached a bottom plate 12 of the filter element having an annular vertical wall 13 surrounding the outer rim of the bottom plate. On the bottom plate 12 is placed a grille 14 supporting a fabric 15 that facilitates a vertically upward- directed liquid flow through the fabric 15 against the bottom plate 12 and further through radial openings 16 made thereon to the interior of the center tube 9.

The inner rim 17 and outer rim 18 of the grille are impervious to liquids thus aiding to prevent the liquid being treated from forming a flow channel in a close vicinity of the vertical wall of the filter element.

On fabric 15 is packed a layer of finely pulverized particular ion-exchange resin 19. While the optimal thickness of the resin layer is determined by the selected resin grade and filter application, the layer thickness typically is 10 to 40 mm. The material of fabric 15 is most advantageously a filter fabric or, alternatively, a nanopore or microfilter membrane.

On top of the resin layer 19 is placed a fabric or other planar element 20 acting as a flow distribution plate and elastic support to the resin layer 19. With the help of fabric 20, the volume changes of resiri 19 can be compensated for, whereby channeling of the liquid flow is prevented. Fabric 20 also prevents resin layer 19 from becoming flushed away along with the liquid flow. The fabric 20 can be secured along its rim on top of the resin layer 19, e.g., by means of clamping rings 21 and 22 that are fastened in place, e.g., by locking pins 23. The bottom surface of the rings may have projections, grooves or the like for more secure clamping of fabric 20.

In the exemplary embodiment described above, the inner center tube portion 10 is made shorter than the upper center tube portion 11 , whereby the stacking of the filter elements leaves radial outlet openings 16 free as then the top end of the outer center tube portion 11 can abut the bottom plate 12 of the filter element that has mounted thereon a seal element 24 made of rubber, for instance.

To prepare the apparatus for filtration, the pressure vessel 1 is opened at flange 5 and a required number of filter elements 4 are stacked atop one another starting from the bottom end of support pipe 6. On top of the stack is placed a guide baffle 8 having the lower end of its center tube shaped in the same fashion as the inner center tube portion 10 of filter element 4, whereby the guide baffle center tube also seals the top end of the filtrate discharge channel comprised of the stacked filter element center tubes 9. Finally, the pressure vessel 1 is closed at its flange.

The actual filtration process is started by filling pressure vessel 1 via inlet nozzle 2 with the liquid to be purified. Inasmuch as according to the invention at least a portion of resin layer 19 must consist of finely pulverized resin, the flow resistance of the resin layer becomes relatively high. As a result, the liquid being purified begins to flow in significant amounts through the resin layer only after the vessel 1 has been filled with the liquid being purified and the pressure in the vessel has arisen sufficiently high. The upper section of vessel 1 may additionally incorporate a venting valve for removal of residual air from the vessel. The venting valve 25 also facilitates filling the vessel 1 at ambient pressure.

During the filtration process, the liquid to be purified is passed under pressure into the vessel 1 , whereby the liquid flows through the resin layer 19 via liquid discharge pipe 3 to the exterior side of vessel 1.

After the ion-exchange resin has been exhausted, it can be regenerated in the vessel using a technique developed for the application. In the regeneration and flushing of the resin bed, the amounts of regeneration/flushing solutions are kept as small as possible and, moreover, a facility should be provided allowing emptying the apparatus from liquid between the different regeneration steps. Herein, however, the resin bed should not be allowed to become dry inasmuch as then cracking and channeling of the resin bed may occur. To keep the resin bed moist, the center tubes 9 of each one of the filter elements are provided with an overflow trough 27 that keeps the liquid level at ail times above the top of the resin bed.

The vessel 1 may also be emptied via, e.g., bottom valve 26 and thereupon opened at joint 5, whereupon the filter elements 4 can be replaced with new elements or refilled with fresh resin.

Inasmuch as the particle size of resin 19 is very small, the resin becomes tightly compacted thus invoking a high flow resistance. Owing to its large filter area, the apparatus is capable of treating large volumes of liquids even at low flow velocities. The filter construction according to the invention is also very conservative over the prior art in regard to its minimal footprint as compared with its liquid treatment capacity.

Typically, the outer surface area of finely pulverized resin is 30- to 40-fold in regard to the outer surface area of an equivalent resin of spherical bead particles. As a result, the finely pulverized resin can adsorb large molecules and colloids that are not capable of penetrating into the pores of spherical bead resin particles or have a slow diffusion into the pores of the resin.

Now the apparatus construction according to the invention can accommodate large variations in the inlet flow by virtue of having the resin layer placed on a horizontal surface and resin layer being protected by the fabric 20 thus preventing the fall-off of the resin even at a complete cut-off of the inlet flow.

Example 1

Lignosulfonates are surface-active substances that, while being able to adsorb easily on different types of surfaces, also readily cause fouling of catalysts. While these compounds in principle can bind on anionic ion-exchange resins, due to their large spherical molecular structure (dia. about 50 A), their molecules cannot penetrate the pores of conventional ion-exchange resins. Equilibrium tests performed in laboratory scale were performed to compare a finely pulverized anion-exchange resin having functional OH- groups and a conventional spherical bead resin (Amberlite IRA410) with each other. The binding capacity of pulverized resin was max. 180 mg lignosulfonate/gram resin. The respective binding capacity of spherical bead resin was 7 mg/gram resin. While changing the liquid temperature from 15°C to 35°C did not appear to influence the binding capacity, some acceleration of binding kinetics was detected. The test proved that finely pulverized resin is superior to spherical bead resin in binding large molecules such as those of lignosulfonates.

The apparatus according to the invention was tested in the filtration of three different production-plant-grade aqueous solutions containing a fine chemical that shall be subjected to hydrogenation. Since the solution also contained impurities in the form of small but varying amounts of lignosulfonates, these have to be removed from the solution prior to hydrogenation inasmuch as otherwise the lignosulfonates will cause fouling of the hydrogenation catalyst. The liquid samples containing 10, 50 and 100 ppm lignosulfonate, respectively, were purified with the help of an apparatus according to the invention using a 40 mm thick resin bed of a finely pulverized anionic ion-exchange resin having functional OH- groups. The respective lignosulfonate concentrations of the outlet filtrates were 0.064, 1.609 and 2.253 ppm. A reference test was also carried out using a 1 m high ion-exchange resin column filled with Amberlite IRA-410 spherical bead ion-exchange resin. The impurity binding capacity of this ion-exchange column was found nonexistent.

Example 2

This laboratory-scale test was performed to examine the removal of a floatation agent (dialkyi dimethyl ammonium chloride) from an aqueous solution. The ion- exchange resin types used in the test comprise the resins listed below, all of which having a styrene divinylbenzene copolymer (PS-DVB) matrix:

PS-DVB cationic ion-exchange resin [H⁺], gelled, sulfonated, bead size d_min >200 μm, 4 % DVB crosslinkage

PS-DVB cationic ion-exchange resin [H⁺], gelled, sulfonated, bead size d_min >400 μm, 8 % DVB crosslinkage PS-DVB cationic ion-exchange resin [H⁺], gelled, sulfonated, pulverized to an average particle size d_p <100 μm, 4 % DVB crosslinkage PS-DVB cationic ion-exchange resin [H⁺], gelled, sulfonated, pulverized to an average particle size d_p <100 μm, 8 % DVB crosslinkage.

The adsorption rate of a large amine molecule on an ion-exchange resin is very slow and requires a retention time of several hours to obtain full economical utilization of the binding capacity of the resin. In the treatment of large liquid volumes like those encountered in a floatation process, for instance, such long treatment retention times are out of question. In contrast, a finely pulverized ion- exchange resin offers immediate economical deployment of the resin such that a liquid retention time of only few tens of minutes in the resin bed is enough. As a result, shallower resin beds can be used in pre-coat filter systems.

The apparatus according to the invention was used to filter an aqueous solution containing 4.9 ppm Armoflote 18 floatation agent. The filtration rate was varied in the range 0.42 - 2.28 m/h. The test was carried out on ion-exchange resin bed thicknesses of 10 and 30 mm, and the filtration test results are shown in FIG. 3.

The regeneration of the resin was possible up to an efficiency of 90 % using an aqueous solution containing 10 % CaCI₂ and 50 % ethanol.

Example 3

In these laboratory-scale tests, 5 wt-% of finely pulverized calcium carbonate (d = 2 μm) was suspended in methanol. Under normal conditions, such colloidal suspension of calcium carbonate does not settle at all. When a strong acid cationic resin having H⁺- functional groups on a styrene divinylbenzene matrix (PS-8%DVB) and pulverized to an average particle size of 75 μm was added to the above suspension, the settling of calcium carbonate was detected at a rate that was proportional to the mutual weight-to-weight ratio of the resin and the calcium carbonate. This test proves that a functionalized ion-exchange resin operates with electrical charges also in organic solutions, whereby the purification of colloidal solutions free from colloidal particles is possible using an ion-exchange resin having functional groups with electrical charges opposite to those of the colloidal particles. An application of the apparatus according to the invention to the purification of a hexane-based industrial process solution of about 5 % solids at 60°C temperature was carried out using the above-mentioned PS-8%DVB cationic ion- exchange resin. Of the process solution solids, a major portion (organic components) were in dissolved form while the inorganic components were either dissolved or in colloidal form. The proportion of the inorganic components (that is, ash content after incineration at 600°C) in the solids was about 0.3 %, a major portion thereof being calcium carbonate. Different amounts of pulverized cationic ion-exchange resin was mixed with the solution, whereupon the resin was separated by filtration. Hexane was separated from the solution by evaporation, and the solids were incinerated at 600°C. The test run results in regard to the solids ash content after these steps are shown in FIG. 4. The mass proportion of the different components in the solids are shown in FIG. 5 wherefrom it can be seen that not only is calcium carbonate removed almost completely but also certain other inorganic compounds have been purified away from this process solution.

To examine the operation of the resin bed, the above solution was treated in a continuous process using an apparatus according to the invention having a total filtration area of 0.5 m² whereon 7 kg of the above-described finely pulverized cationic ion-exchange resin was applied in moistened form. The solution to be treated was fed at a continuous flow rate of 4 m³/h during 4 hours. The liquid flow was stopped once at each two hours allowing the apparatus to stabilize, whereupon the flow was restarted. A differential pressure sensor was installed to monitor pressure drop over one of the ion-exchange resin beds. The test results were as follows:

Time Ash content Pressure drop

40 min 0.06 wt-% 2.1 bar 110 min 0.07 wt-% 2.7 bar

170 min 0.06 wt-% 2.7 bar

250 min 0.04 wt-% 2.9 bar

This example proves that finely pulverized ion-exchange resins can be used for removal of colloidal or dissolved inorganic components from an organic solvent. The present invention provides lower ash contents in the dry solids than other examined purification methods such as crystallization. It is furthermore essential to appreciate the benefit of the embodiment according to the invention that allows stopping the liquid without causing any degradation of purification capacity at the restart of the filtration flow.

Example 4

An apparatus in accordance with the present exemplary embodiment was used for removing colorants from an alcoholic product. The colorants were chiefly anthocyanin compounds stemming from the grape skins. The tests were carried out using both finely pulverized resin prepared milling commercially available spherical bead XAD-4 polymeric adsorbent (manufacturer Rohm and Haas Co.) and ready pulverized (10 μm) Polyspher PST10 spherical bead polymeric adsorbent (manufacturer Merck KGaA). Each of these polymeric adsorbents are macroporous nonfunctionalized styrene polymers crosslinked with divinylbenzene.

Each one of the adsorbents was tested as a bed about 30 mm high. The efficiency of colorant removal was monitored by measuring the absorption of visible light in the alcohol with the help of a spectrophotometer. In each one of the exemplary adsorbent tests, measurements at 420 nm and 510 nm wavelengths gave absorbance values smaller than 1 % of those measured from the inlet solutions.

To a person versed in the art it is obvious that the invention is not limited to the exemplary embodiment discussed above, but rather can be varied without departing from the scope and spirit of the invention disclosed in the appended claims. The benefits of the above-described application are attained using a finely pulverized polymeric resin having an average particle size smaller than 200 μm, preferably smaller than 100 μm. The resin may be functionalized or nonfunctionalized. In the latter case, the resin may be in any ionic form. Neither is the type and method of fabrication of the ion-exchange resin restricted in any way. Furthermore, the resin bed may contain more than one ion-exchange resin type in a mixed, layered or otherwise combined bed. The resin bed may also contain inert components such as fiber for controlling the flow resistance or other mechanical properties of the bed. The impurity-removing effect occurring in the solution treatment according the present method is based on surface adsorption, ion exchange, ion exclusion and/or ion inclusion.

For trapping resin particles escaped from the bed, the discharge pipe of the pressure vessel may be additionally equipped with a supplementary filter.

The above-described embodiment has the resin packed between two fabrics or membranes of which the upper one is secured with the help of clamping rings fastened with locking pins. Both or only one of these fabrics or membranes may also impart a mechanical filtration effect.

The resin bed may alternatively be a ready-packed planar disc insertable into the filter element. This kind of discoidal resin bed element can be comprised of, e.g., fabrics, perforated plates or the like members located to both sides of the resin bed and fastened at their rims to plastic rings, for instance. It is also possible to fasten the fabrics at their rims by means of a castable polyurethane compound. The resin bed disc may additionally incorporate required seal elements that prevent bypass flow past the filter element.

While the filter elements of the above-described exemplary embodiment are designed replaceable for easy servicing and installation, the filter elements may obviously form an all-inclusive integral entity.

Furthermore, the application of the present method is not limited to the above- described exemplary embodiments, but rather, may also be utilized in the separation of large molecules and material aggregates such as proteins, polymers and substances occurring in colloidal and gel form.

Claims

What is claimed is:

1. A method for treating liquids, particularly by means of an apparatus based on the use of an ion-exchange resin, characterized in that the liquid to be treated is passed into a vessel (1 ), wherein the liquid is treated by flowing the liquid into at least one horizontally mounted filter element (4) containing a thin layer of an ion- exchange resin and, after being thus treated, the liquid is passed to the exterior side of the vessel (1 ).

2. The method of claim 1 , characterized in that in the method the liquid is passed into a pressure vessel (1), wherein said horizontal filter elements (4) are mounted into a vertical stack (7) suitable for treating the liquid by passing the same through thin layers of finely pulverized ion-exchange or adsorbent material layers (19).

3. The method of claim 1 or 2, characterized in that in the method, in order to prevent cracking and channeling of the resin bed, the ion-exchange resin layers (19) are kept continuously moist with the help of, e.g., an overflow trough (27) or the like arrangement.

4. The method of claims 1 - 3, characterized in that the pressure vessel (1 ) is operated pressurized in the range 0 - 30 bar and on the upper surface of the filter element (4) employed in the purification of the liquid is formed a layer about 10 - 100 mm, advantageously 10 - 40 mm thick of entirely or in part finely pulverized ion-exchange resin having a particle size of 1 - 300 μm, typically 10 - 300 μm, whereby the average particle size is advantageously less than 200 μm, most advantageously less than 100 μm.

5. The method of claims 1 - 4, characterized in that the impurity-removing effect occurring in the solution treatment is based on surface adsorption, ion exchange, ion exclusion and/or ion inclusion.

6. An apparatus for treating liquids, particularly implemented as an apparatus based on the use of an ion-exchange resin, characterized in that into a pressure vessel (1 ) of the apparatus is adapted at least one horizontal filter element (4) containing a thin layer of an ion-exchange resin.

7. The apparatus of claim 6, characterized in that into the pressure vessel (1 ) are adapted the horizontal filter elements (4) used for liquid purification so that the filter elements form a contiguous stack (7) suitable for treating the liquid.

8. The apparatus of claim 6 or 7, characterized in that the filter elements (4) are placed on one another onto a support tube (6) so as form the vertical stack (7) on which finally is placed a guide baffle (8).

9. The apparatus of claims 6 - 8, characterized in that the center tube (9) of the filter element (4) comprises an inner center tube portion (10) and an outer center tube portion (11) so dimensioned that a contiguous stack (7) is formed by fitting the inner center tube portion (10) of one element into the outer center tube portion (11 ) of the next element (4) below.

10. The apparatus of claims 6 - 9, characterized in that the filter element (4) comprises a bottom plate (12) attached to the center tube (9), the bottom plate having an annular vertical rim wall (13), a grille (14) placed on the bottom plate (12) and a fabric (15).

1 1. The apparatus of claims 6 - 10, characterized in that the inner rim (17) and the outer rim (18) of the grille (14) are impervious to liquids.

12. The apparatus of claims 6 - 11 , characterized in that onto the fabric (15) placed in the filter element (4) is packed a layer (19) of an ion-exchange resin having a fabric and/or a plate (20) placed thereon and clamped in place by means of clamping rings (21) and (22) that are secured by locking pins (23), for instance.

13. The apparatus of claims 6 - 12, characterized in that the inner center tube portion (10) is made shorter than the outer center tube portion (11 ) in order to leave free space for an outlet opening (16).

14. The apparatus of claims 6 - 13, characterized in that the fabric (15) is a filter fabric or a nanopore or microfiltration membrane.

15. The apparatus of claims 6 - 14, characterized in that, in order to prevent cracking and channeling of the resin bed, the ion-exchange resin layers (19) are kept continuously moist with the help of, e.g., an overflow trough (27) or the like arrangement.

16. The apparatus of claims 6 - 15, characterized in that the pressure vessel (1 ) of the apparatus is operated pressurized in the range 0 - 30 bar and on the upper surface of the filter element (4) employed in the purification of the liquid, onto the fabric (15), is formed a layer about 10 - 100 mm, advantageously 10 - 40 mm thick of entirely or in part finely pulverized ion-exchange resin having a particle size of 1 - 300 μm, typically 10 - 300 μm, whereby the average particle size is advantageously less than 200 μm, most advantageously less than 100 μm.