阅读说明：本技术 回收聚酰胺6的生产中的萃取水的方法 (Method for recovering extraction water in the production of polyamide 6 ) 是由 约翰内斯·凯泽 于 2018-06-01 设计创作，主要内容包括：本发明涉及一种对在聚酰胺6或其共聚物的生产中产生的萃取水进行回收的方法,所述方法包括以下步骤：a)用至少一个过滤单元过滤所述萃取水；b)在离子交换模块中净化过滤后的所述萃取水,所述离子交换模块至少包括以下离子交换单元：i)至少一个阳离子交换单元,ii)至少一个阴离子交换单元,其中,所述萃取水以i–ii的顺序流过所述离子交换单元；c)通过iii)至少一个阳离子交换单元或包括至少一种阴离子交换剂和至少一种阳离子交换剂的混合离子交换单元对来自步骤b)的所述萃取水除臭,在整个方法中,所述萃取水的温度范围为80至100℃。本发明还涉及用于执行根据本发明的方法的装置和所述装置的使用方法。(The invention relates to a method for recovering extraction water produced in the production of polyamide 6 or copolymers thereof, comprising the following steps: a) filtering the extract water with at least one filtration unit; b) purifying the filtered extract water in an ion exchange module, the ion exchange module comprising at least the following ion exchange units: i) at least one cation exchange unit, ii) at least one anion exchange unit, wherein the extract water flows through the ion exchange units in the order i-ii; c) deodorizing the extract water from step b) by iii) at least one cation exchange unit or a mixed ion exchange unit comprising at least one anion exchanger and at least one cation exchanger, the temperature of the extract water in the overall process being in the range of 80 to 100 ℃. The invention also relates to a device for carrying out the method according to the invention and to a method for using said device.)

1. A process for recovering extraction water produced in the production of polyamide 6 or copolymers thereof, said process comprising the steps of:

a) filtering the extract water with at least one filtration unit,

b) purifying the filtered extract water in an ion exchange module, the ion exchange module comprising at least the following ion exchange units:

i) at least one of the cation exchange units is,

ii) at least one anion exchange unit,

wherein the extract water flows through the ion exchange unit in the order of i-ii,

c) by passing

iii) at least one cation exchange unit or a mixed ion exchange unit comprising at least one anion exchanger and at least one cation exchanger

Deodorizing the extract water from step b), and

wherein the temperature of the extraction water ranges from 80 to 100 ℃ in the whole process.

2. The method of claim 1,

the extract water contains caprolactam in monomeric form and/or cyclic and/or linear oligomers of caprolactam and impurities, preferably selected from the group consisting of titanium compounds, silicon compounds, manganese compounds, aluminum compounds, sodium compounds, potassium compounds, calcium compounds, in particular calcium sulfate, calcium polyphosphate, calcium oligophosphate and mixtures thereof, wherein preferably

The proportion of cyclic and/or linear oligomers of caprolactam is from 5 to 20%, preferably from 10 to 15%, and/or by weight, based on the total mass of the extract water

The proportion of caprolactam is 5 to 20%, preferably 10 to 15%, and/or based on the total mass of the extract water by weight

The proportion of impurities in the extraction water is less than 1%, preferably less than 0.5% by weight, based on the total mass of the extraction water.

3. The method according to claim 1 or 2,

the temperature of the extract water is in the range of 83 to 95 c, preferably in the range of 85 to 90 c, throughout the process.

4. The method according to any of the preceding claims,

the filter unit a) comprises a filter having a pore size in the range of 0.1-100 μm, preferably 5-50 μm.

5. The method according to any of the preceding claims,

the at least one cation exchange unit i) is arranged in the form of a resin bed, and/or

Containing a cation exchange resin based on sulfonic acid groups, and/or

Is by-passable, and/or

Interchangeable with a second cation exchange unit by activation of a switch, preferably, said second cation exchange unit is identical in design and ion exchange material to said first cation exchange unit,

the at least one anion exchange unit ii) is arranged in the form of a resin bed, and/or

Containing an anion exchange resin based on trimethylammonium groups, and/or

Is by-passable, and/or

The second anion exchange unit is interchangeable with the second anion exchange unit by activation of a switch, preferably the second anion exchange unit is identical in design and ion exchange material to the first cation exchange unit.

6. The method according to any of the preceding claims, characterized in that the at least one cation exchange unit or the mixed ion exchange unit iii) used in step c) is configured in the form of a resin bed, preferably the resin bed is arranged in the ion exchange module comprising the ion exchange units i) and ii), and/or

A mixture comprising a sulfonic acid group-based cation exchange resin and a trimethylammonium group-based anion exchange resin.

7. The method according to any one of claims 1 to 5,

subjecting the purified extract water from step b) to a deodorization step by means of at least one vessel filled with a cation exchange resin or a mixture of at least one cation exchanger resin and at least one anion exchange resin, wherein preferably the cation exchange resin is based on sulfonic acid groups and preferably the anion exchange resin is based on trimethylammonium groups.

8. The method of claim 7,

the container being by-passable, and/or

The container is interchangeable with a second container by activating a switch, preferably the second container is identical in design and ion exchange material to the first container.

9. The method of claim 7 or 8, wherein the at least one container is mounted between the ion exchange module and the evaporation system, wherein

The conductivity of the extract water after step c) is lower than 10 μ S/cm, preferably lower than 5 μ S/cm, and more preferably lower than 1 μ S/cm.

10. Method according to claim 7 or 8, characterized in that the at least one vessel is arranged between the evaporation system and the extractor, preferably in the condensate of the evaporation system.

11. The method according to any of the preceding claims,

at least one of the ion exchange units i), ii) or iii), preferably all of the ion exchange units and/or the at least one vessel, comprises at least one protective filter.

12. An apparatus for purifying and deodorizing caprolactam-containing extraction water produced in the production of polyamide 6 or copolymers thereof, comprising an upstream extractor (4) and a concentration device (9) arranged downstream thereof, at least one filtration unit (6) and an ion exchange module (7) being located between the upstream extractor (4) and the concentration device (9) in the flow direction, wherein the ion exchange module (7) comprises at least the following ion exchange units:

i) at least one of the cation exchange units is,

ii) at least one anion exchange unit,

iii) at least one cation exchange unit or a mixed ion exchange unit comprising at least one anion exchanger and at least one cation exchanger, and

wherein the ion exchange units are arranged in the order of i-ii-iii in the flow direction of the extract water.

13. The apparatus of claim 12,

the at least one cation exchange unit i) is arranged in the form of a resin bed, and/or

Containing a cation exchange resin based on sulfonic acid groups, and/or

The at least one anion exchange unit ii) is arranged in the form of a resin bed, and/or

Containing an anion exchange resin based on trimethylammonium groups, and/or

The at least one cation exchange unit or the mixed ion exchange unit iii) is configured in the form of a resin bed or a vessel, and/or

A mixture comprising a sulfonic acid group-based cation exchange resin and a trimethylammonium group-based anion exchange resin, and/or

At least one, preferably all, of the ion exchange units i), ii) and iii) may be bypassed, and/or

At least one, preferably all, of the ion exchange units i), ii) and iii) are interchangeable with a second ion exchange unit by activating a switch, preferably the second ion exchange unit is identical in design and ion exchange material to the first ion exchange unit.

14. Use of the device according to claim 12 or 13 for the recovery of extraction water produced in the production of polyamide 6.

15. Use according to claim 14,

the extract water contains caprolactam in monomeric form and/or cyclic and/or linear oligomers of caprolactam and impurities, preferably selected from the group consisting of titanium compounds, silicon compounds, manganese compounds, aluminum compounds, sodium compounds, potassium compounds, calcium compounds, in particular calcium sulfate, calcium polyphosphate, calcium oligophosphate and mixtures thereof, wherein preferably

The proportion of cyclic and/or linear oligomers of caprolactam is from 5 to 20%, preferably from 10 to 15%, and/or by weight, based on the total mass of the extract water

The proportion of caprolactam is 5 to 20%, preferably 10 to 15%, and/or based on the total mass of the extract water by weight

The proportion of impurities in the extraction water is less than 1%, preferably less than 0.5% by weight, based on the total mass of the extraction water.

16. Use according to claim 14 or 15,

the temperature of the extract water is in the range of 80 to 100 ℃, preferably in the range of 83 to 95 ℃, and, more preferably, in the range of 85 to 90 ℃.

Technical Field

The invention relates to a method for recovering extract water produced in the production of polyamide 6 or copolymers thereof (PA6/66), to a device for recovering extract water produced in the production of polyamide or copolymers thereof (PA6/66), and to the use of the device for recovering extract water produced in the production of polyamide 6 or copolymers thereof (PA 6/66).

Background

In industrial large-scale polyamide 6 production, the polymerized raw product must be washed to remove caprolactam monomer as well as cyclic and linear caprolactam oligomers. Hot water is typically used in the washing. The extraction water produced in the process usually contains 5 to 20% by weight of organic material, which for economic reasons must be reused. For this purpose, the organic material is concentrated and used as starting material for the polyamide 6 process, while the condensed distillate is reused for the extraction.

In the production of polyamide 6, additives, such as titanium dioxide matting agents for textile applications, may have been added during the polymerization. As a result, the subsequent process stages of extraction involve washing away of these additives in contact with water and foreign matter (e.g., minerals from the coating on the titanium dioxide).

To avoid mineral build-up in the recovery line, it is desirable to remove the extracted water minerals directly after extraction. The difficulty with this is that dissolved oligomers of caprolactam precipitate at temperatures below 80 c, which potentially blocks the lines. However, if the temperature is kept above 80 ℃, anion exchangers cannot be used because at temperatures above 80 ℃ they degrade rapidly and release strongly odorous compounds (especially amines) and contaminate the liquid stream to be recovered.

Methods for purifying caprolactam-containing solutions by using ion exchange resins are known from the prior art.

US 5,245,029 relates to an ion exchange process for purifying aqueous-caprolactam solutions in the production of caprolactam and laurolactam, in which a mixture of cyclohexanone oxime and cyclododecanone oxime is subjected to beckmann rearrangement in the presence of sulfuric acid and oleum. The process comprises, after neutralising the rearrangement reaction product, a first extraction with an organic solvent and a second extraction of the first extract with water to obtain a second extract of aqueous caprolactam solution. The aqueous caprolactam solution obtained by extraction with a water-immiscible organic solvent is treated with a strongly acidic cation exchange resin and then with a weakly basic anion exchange resin or with a strongly basic anion exchange resin to remove surface-active substances, such as alkyl sulfates.

GB 762,879 describes a process for removing organic impurities from lactams which describes the step of passing the lactams in aqueous solution through anion and cation exchangers, which may be arranged in any desired order.

GB 1,175,279 relates to a process for purifying caprolactam obtained by nitrosation of a cyclohexyl compound, said caprolactam containing a volatile amide-based base. For this purpose, caprolactam is treated with an alkaline agent in the presence of water and a halogen or alkali metal hypohalide in order to convert the volatile amide-based base into an amine compound. These amine compounds are separated from caprolactam, for example, by means of a cation exchanger.

US 5,225,524 relates to a method of making an amino group-containing polymer solution odorless. In one embodiment, a solution of a terpolymer of vinylpyrrolidone, vinylcaprolactam, and dimethylaminoethyl methacrylate is treated with 0.1 to 10% by weight of an acidic compound or an acidic anion exchange resin to render the solution substantially odorless.

However, these processes either do not work at temperatures above 80 ℃ so that the caprolactam oligomer does not remain in solution or no anion exchanger is used.

Disclosure of Invention

Against this background, the problem to be solved by the present invention is to provide a process by which any precipitation of caprolactam oligomer and removal of soluble cationic and anionic impurities is reliably prevented without rapid degradation of the resin and without release of strongly odorous substances. Suspended and insoluble materials are further removed. The problem addressed by the present invention is also to provide an apparatus for purifying the extract water produced in the production of polyamide 6 or its copolymers.

This problem is solved by a method according to independent claim 1, comprising the steps of:

a) filtering the extract water with at least one filtration unit,

b) purifying the filtered extraction water in an ion exchange module, wherein the ion exchange module at least comprises the following ion exchange units:

i) at least one of the cation exchange units is,

ii) at least one anion exchange unit,

wherein the extraction water flows through the ion exchange unit in the order of i-ii,

c) by passing

iii) at least one cation exchange unit or a mixed ion exchange unit comprising at least one anion exchanger and at least one cation exchanger

Deodorizing the extract water from step b),

wherein the temperature of the extraction water is in the range of 80 to 100 ℃ throughout the process.

Preferred embodiments of the method according to the invention are described in the dependent claims 2-11.

Independent claim 12 also relates to an apparatus for purifying and deodorizing caprolactam-containing extract water produced in the production of polyamide 6, comprising an upstream extractor and a concentrating device arranged downstream thereof, at least one filtration unit and an ion exchange module being located between the upstream extractor and the concentrating device in the flow direction, wherein the ion exchange module comprises at least the following ion exchange units:

i) at least one of the cation exchange units is,

ii) at least one anion exchange unit,

iii at least one cation exchange unit or a mixed ion exchange unit comprising at least one anion exchanger and at least one cation exchanger, and

wherein the ion exchange units are arranged in the order of i-ii-iii in the flow direction of the extraction water.

Preferred embodiments of the device according to the invention are described in the dependent claim 13. Claims 14 to 16 relate to the use of the device according to the invention for the recovery of extraction water produced in the production of polyamide 6.

For the purposes of the present invention, "recovery" of the extract water is understood to mean the return of a concentrate of the extract water to the polymerization reactor to produce polyamide 6.

For the purposes of the present invention, "purification" relates to the step of removing soluble and insoluble impurities from the extraction water.

"deodorization" according to the invention is understood to mean a step of removing from the extract water strongly odorous substances formed in the "purification" step or not removed in the purification step.

The ion exchange resin has functional groups such as sulfonic acid groups, trimethylammonium groups, or amino groups. For the purposes of the present invention, an ion exchange resin based on functional groups is understood to mean that the functionality of the ion exchange resin is located on the group.

Method of producing a composite material

A preferred embodiment of the invention provides that the extract water contains caprolactam and/or cyclic and/or linear oligomers of caprolactam in monomeric form and impurities, preferably selected from the group consisting of titanium compounds, silicon compounds, manganese compounds, aluminum compounds, sodium compounds, potassium compounds, calcium compounds, in particular calcium sulfate, calcium polyphosphate, calcium oligomeric phosphates and mixtures thereof.

In another preferred embodiment of the invention, the proportion of cyclic and/or linear oligomers of caprolactam is from 5 to 20%, preferably from 10 to 15%, by weight, based on the total mass of the extract water.

A particularly preferred embodiment of the invention provides that the extract water contains caprolactam and/or cyclic and/or linear oligomers of caprolactam in monomeric form and impurities, preferably selected from the group consisting of titanium compounds, silicon compounds, manganese compounds, aluminum compounds, sodium compounds, potassium compounds, calcium compounds, in particular calcium sulfate, calcium polyphosphate, calcium oligophosphate and mixtures thereof, and that the proportion of cyclic and/or linear oligomers of caprolactam is from 5 to 20%, preferably from 10 to 15%, by weight, based on the total mass of the extract water

In a preferred embodiment of the invention, the proportion of caprolactam is from 5 to 20% by weight, preferably from 10 to 15% by weight, based on the total mass of extract water.

In another preferred embodiment of the invention, the proportion of impurities in the extraction water is less than 1% by weight, preferably less than 0.5% by weight, based on the total mass of the extraction water.

Another preferred embodiment of the invention provides that the temperature of the extraction water is in the range of 83 to 95 c, preferably in the range of 85 to 90 c, throughout the process. If lower temperatures are used, oligomers of caprolactam precipitate and may clog lines.

In another preferred embodiment of the invention, the filter unit a) comprises a filter having a pore size in the range of 0.1 to 100 μm, preferably 5 to 50 μm. The filtration unit removes insoluble impurities and suspended matter from the extraction water.

In another preferred embodiment of the invention, at least one cation exchange unit i) is configured in the form of a resin bed.

Another preferred embodiment of the invention provides that at least one cation exchange unit i) comprises a sulfonic acid group-based cation exchange resin. The sulfonic acid group-based cation exchange resin is strongly acidic.

In another preferred embodiment of the invention, at least one anion exchange unit ii) is configured in the form of a resin bed.

In another preferred embodiment of the present invention, at least one anion exchange unit ii) comprises an anion exchange resin based on trimethylammonium groups. Trimethyl ammonium based anion exchange resins are calculated as type I exchangers, have strong basicity and higher thermal stability compared to type II exchangers. Amino-based anion exchange resins are counted as being weakly basic anion exchange resins.

A further preferred embodiment of the invention provides that at least one cation exchange unit or mixed ion exchange unit iii) used in step c) for deodorization is configured in the form of a resin bed. Thus, for example, a mixed bed is used, and the cation and anion exchange resins form an almost uniform distribution in the mixed bed. There is no limitation with respect to the mixing ratio between the cation and anion exchange resins. The preferred ratio of cation exchange resin to anion exchanger based on active groups is 1.9: 1.3.

in a preferred embodiment, the ion exchange unit iii) is present in the ion exchange module together with the ion exchange units i) and ii).

In another preferred embodiment of the present invention, at least one of the mixed ion exchange units comprises a mixture of a sulfonic acid group-based cation exchange resin and a trimethylammonium group-based anion exchange resin.

In another preferred embodiment of the present invention, the deodorization step according to step c) is ensured by at least one vessel filled with a cation exchange resin or a mixture of at least one cation exchange resin and at least one anion exchange resin. Preferably, the vessel is installed downstream of the ion exchange module in the extraction water circuit. The deodorization step c) serves to neutralize the odor-intensive substances which are sometimes newly formed by the ion exchange module, in particular the ion exchange unit ii).

In another preferred embodiment of the invention, preferably the cation exchange resin in the vessel is based on sulfonic acid groups and the anion exchange resin is based on trimethylammonium groups.

In another preferred embodiment of the invention, at least one container is mounted between the ion exchange module and the evaporation system.

A further preferred embodiment of the invention provides that at least one container for deodorization is arranged between the evaporation system and the extractor. It is particularly preferred to arrange the container in the condensate of the evaporation system, since the temperature there is relatively low, 20 to 70 c, preferably 40 to 60 c. This has the advantage that the ion exchange resin is subjected to lower thermal stress and can therefore be used for a longer period of time. Another reason why it is preferred to install the container in the condensate of the evaporation system is that volatile amines, which are strongly odorous substances, accumulate there because they evaporate with the water.

The water returned from the evaporation system to the extractor does not contain any organic components, such as caprolactam monomer or caprolactam oligomer.

Another preferred embodiment of the invention provides that at least one, preferably all, of the ion exchange units i), ii) or iii) for deodorization comprise at least one protective filter.

In a preferred embodiment of the invention, at least one, preferably all, of the ion exchange units i), ii) and iii) are by-passable.

In a further preferred embodiment of the invention, at least one, preferably all, of the ion exchange units i), ii) and iii) are interchangeable with a second ion exchange unit by means of an activation switch, preferably the second ion exchange unit is identical to the first ion exchange unit in terms of design and ion exchange material.

Being temporarily bypassed or exchanged with the second vessel and/or the second ion exchange unit makes it possible to exchange the ion exchange resin without having to interrupt operation.

In a preferred embodiment of the invention, the container has at least one protective filter, it being particularly preferred to provide the protective filter not only for the inlet but also for the outlet of the container.

The purpose of the protective filter is to prevent the entrainment of foreign matter into the ion exchange resin. It is particularly preferred that the ion exchange unit last in the flow direction has a protective filter on the outflow side to prevent mechanical debris from entering the ion exchange resin bed and from being entrained into the process circuit.

A further preferred embodiment of the method according to the invention provides that after step c) the conductivity of the extract water is below 10 μ S/cm, preferably below 5 μ S/cm, more preferably below 1 μ S/cm, which step is performed between the ion exchange module comprising i) and ii) and the evaporation system.

Device and method of use thereof

In a preferred embodiment of the invention, the apparatus is configured such that at least one cation exchange unit i) is configured in the form of a resin bed and/or comprises a sulfonic acid group based cation exchange resin, and/or

The at least one anion exchange unit ii) is configured in the form of a resin bed and/or comprises an anion exchange resin based on trimethylammonium groups and/or comprises a mixture of a cation exchange resin based on sulfonic acid groups and an anion exchange resin based on trimethylammonium groups.

The device according to the invention is used in particular for recovering extraction water produced in the production of polyamide 6.

In a preferred embodiment of the invention the apparatus is used for recovering extract water containing caprolactam and/or cyclic and/or linear oligomers of caprolactam in monomeric form and impurities, preferably selected from the group consisting of titanium compounds, silicon compounds, manganese compounds, aluminum compounds, sodium compounds, potassium compounds, calcium compounds, in particular calcium sulfate, calcium polyphosphate, calcium oligomeric phosphates and mixtures thereof. The proportion of cyclic and/or linear oligomers of caprolactam is from 5 to 20% by weight, preferably from 10 to 15% by weight, based on the total mass of the extract water. The proportion of caprolactam is from 5 to 20% by weight, preferably from 10 to 15% by weight, based on the total mass of the extract water. The proportion of impurities in the extract water is less than 1%, preferably less than 0.5%, by weight, based on the total mass of the extract water.

In another preferred embodiment of the invention, the device is used for recovering extraction water having a temperature in the range of 80 to 100 ℃, preferably in the range of 83 to 95 ℃ and more preferably in the range of 85 to 90 ℃.

Drawings

Fig. 1 to 3 are intended to better illustrate the invention, but are in no way to be construed as limiting in any way.

Detailed Description

Figure 1 shows a schematic process of a polyamide 6 production process comprising a waste water extraction circuit. A filtration unit (6) and an ion exchange module (7) comprising a cation exchange unit (i) and an anion exchange unit (ii) are located between the extractor (4) and the evaporation system (9). The units (6) and (7) ensure filtration and purification according to process steps a) and b). The container (8) is filled with ion exchange resin and comprises a cation exchange unit or a hybrid ion exchange unit iii for deodorization according to method step c), which container (8) can be arranged between the ion exchange module (7) and the evaporation system (8'). Preferably, however, the container is placed between the evaporation system and the extractor, more preferably in the condensate of the evaporation system (8 "). Two or more containers may also be used for deodorization.

Fig. 2 shows in schematic form the flow of the mineral-containing extract water (15) which is passed successively through a filtration unit (6), a cation exchanger (7a) i) and an anion exchanger (7b) ii) to obtain a low-mineral extract water (16), which low-mineral extract water (16) is returned to the production process of polyamide 6. Alternatively, the ion exchange unit (8) iii) comprising a hybrid ion exchange unit may be installed directly downstream of the ion exchange units (7a) and (7 b).

Fig. 3a shows a by-passable version of the container (8) for deodorization, while fig. 3b shows an embodiment comprising a switchable second container. Fig. 3c shows an embodiment of a switchable design of the same ion exchange unit comprising a cation exchange unit i), an anion exchange unit ii) and an ion exchange unit iii) for deodorization.

List of reference numerals:

1 caprolactam mixture, and optionally adding a copolymer monomer

2 reactor

3a Polyamide 6 sheet (after production)

3b Polyamide 6 sheet (after extraction)

3c Polyamide 6 sheet (after drying)

4 extractor

5 extraction water

6 Filter unit

7 ion exchange module

8 Container for deodorization with ion exchange resin ('and' means different positions)

9 vaporization system

10 evaporated water

11 concentration of extract water

12 caprolactam and its oligomers returning to the reactor

13 dryer

14 water and solid waste

15 mineral-containing extraction water

16 extraction water with low mineral content

17 protective filter (a and b show different positions)

Experimental part

The following examples are intended to better illustrate the invention without having any limiting effect.

The ion exchange resins used in the examples have been regenerated prior to use and/or may be used commercially directly.

Removal of trimethylamine by ion exchanger mixed bed

Strongly basic anion exchange resin form I (100g) was refluxed overnight in water (200 g). Subsequently, the water had an unpleasant fishy taste, whereas trimethylamine was detected by gas chromatography. The resulting water was treated with a mixed bed consisting of strong acid ion exchange resin and strong base ion exchange resin for 5 minutes (3 parts water per 1 part mixed bed) (for 5 minutes), after which the odor disappeared and trimethylamine was no longer detected.

Heat treatment of mixed beds of ion exchangers

A mixed bed consisting of strong acid and strong base ion exchangers (100g) was refluxed in water (200g) for 2 days. No noticeable bad smell was observed and no trimethylamine was detected.

Removal of soluble impurities by a series of ion exchangers

An aqueous solution having an electrical conductivity of 32. mu.S/cm was passed through the resin beds of the type I strong acid cation exchanger and the strong base anion exchanger in this order. The conductivity in the solution decreased to 3-4. mu.S/cm during the process. Subsequently, the conductivity is further reduced to 0.4 to 0.5. mu.S/cm by passage through a mixed bed consisting of a strong acid type I and a strongly basic ion exchanger.