FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
A METHOD FOR TREATMENT OF ION EXCHANGE RESINS FOR RESTORATION OF ION EXCHANGE CAPACITY
RELIANCE INDUSTRIES LIMITED
an Indian Company of Maker Chambers IV, Nariman Point, Mumbai - 400021, Maharashtra, India Inventors:
1. SHOWN BISWAJIT
2. GHOSH SWAPAN 3.DASASITKUMAR

4. SALGARKAR SUYOG SUBHASH
5. BAISHYA MUKUNDA MADHAV
6. LADANI MITUL AMRUTBHAI
7. PANSERIYA CHIRAG DALPATBHAI
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE DISCLOSURE:
The present disclosure relates to a method for treatment of ion exchange resins. Particularly, the present disclosure relates to a method for treatment of anion exchange resins for restoration of ion exchange capacity.
BACKGROUND:
Petroleum crude oils contain many impurities such as organic acids and asphaltenes. Amongst these, organic acids i.e., naphthenic acids, are one of the major impurities. Naphthenic acids are highly corrosive and corrode refining process equipment. Generally, naphthenic acid severely cause corrosion at high temperature i.e., 200 to 400 °C. Moreover, due to the presence of polar carboxylic acid groups, low molecular naphthenic acids act as a surfactant and during desalting process they create problem by forming tight water-in-oil emulsion.
Due to the above mentioned processing problems, naphthenic acid removal from crude oil is necessary. There are several methods available for removing acidic components from crude oil including neutralization using oxides or hydroxides of alkali or alkaline earth metals or amine compounds, treatment with zeolites, esterification with alcohols, use of ion-exchange method and the like. Although neutralization or esterification methods are simple to execute, they lead to conversion of acidic portion into non-corrosive metal salts which create problem in the downstream process unit.
However, no harmful byproduct evolved in ion-exchange method. Therefore, it is widely used method for the de-acidification of crude oil.
The ion-exchange resin after it has been spent due to the saturation of acids needs to be activated for restoring ion-exchange capability.
US4037656 discloses a method for removing carboxylic acids from the carboxylic acid containing ion-exchange resin. In the method, carboxylic acid containing ion-exchange resin is contacted with an alcoholic caustic solution to remove carboxylic acid.

However, this method is not satisfactory because it does not remove carboxylic acids efficiently and hence incapable of activating the ion-exchange resin. In view of this, there exists a need for a simple and efficient method for treatment of deactivated resins to restore their ion exchange capacity.
DEFINITION:
As used in the present specification, the following word/s and phrase/s is/are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used indicate otherwise.
The term "adherence" in the context of the specification means any compound or inorganic impurity or organic impurity present in highly acidic crude oil that may attach to the resin through physical force or chemical bond.
OBJECTS:
Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is another object of the present disclosure to provide a method for treatment of ion exchange resin.
It is still another object of the present disclosure to provide a method for treatment of ion exchange resin which efficiently removes trapped heavier hydrocarbons such as resins and asphaltenes.
It is yet another object of the present disclosure to provide a method for treatment of ion-exchange resin which effectively reduces total acid number and trapped inorganic salts present when used for processing crude oil.

It is yet another object of the present disclosure to provide a method for treatment of
ion exchange resin which is simple and economic.
Other objects and advantages of the present disclosure will be more apparent from the
following description which is not intended to limit the scope of the present
disclosure.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING/S:
The disclosure will now be explained in relation to the non-limiting accompanying drawing/s, in which:
FIGURE 1 illustrates the consistency of the resin recycled upto 34 recycles using the method of the present disclosure to process highly acidic crude oil
SUMMARY:
In one aspect of the present disclosure there is provided a method for treatment of at least partially spent ion-exchange resin to restore ion-exchange capacity, said method comprising the following steps:
at least partially removing adherences including asphaltenes, aromatic hydrocarbons, aliphatic hydrocarbons and other resinous materials from said spent ion-exchange resin by contacting said ion-exchange resin with at least one non-acidic crude oil condensate followed by at least one polar organic solvent to obtain partially cleansed ion-exchange resin; and
treating said partially cleansed ion-exchange resin with at least one alkali or alkaline earth metal hydroxide solution followed by iterative washing to remove organic acid trapped in said ion-exchange resin to obtain a treated ion-exchange resin with restored ion exchange capacity.
In one embodiment of the present disclosure the method steps (a) and (b) are carried out in a column.

The method of the present disclosure is characterized in that the proportion of said spent ion-exchange resin and said non-acidic crude oil condensate ranges between 1:1 and 1:10, and the proportion of said spent ion exchange resin and said polar organic solvent ranges between 1: 0.5 and 1:5.
Typically, the non-acidic crude oil condensate is at least one crude oil having boiling point in the range of 35°C and 370°C.
Preferably, the non-acidic crude oil condensate is at least one selected from the group consisting of crude oil condensates, light kerosene, toluene, heavy kerosene and diesel.
Typically, the spent ion-exchange resin is an anion exchange resin. Preferably, the spent ion-exchange resin is a macro porous anion exchange resin comprising: i. at least one functional group selected from the group consisting of benzyl"
trimethyl amine chloride, benzyl dimethyl ethanolamine chloride, tertiary
ammonium chloride and quaternary ammonium chloride; and ii. a resin matrix containing at least one polymer selected from the group
consisting of styrene di-vinyl benzene copolymer and polystyrene co-polymer. Typically, the organic acid is at least one compound represented by R(CH2)n COOH,
Wherein,
R is selected from the group consisting of substituted or un-substituted alkyl
group and substituted or un-substituted cycloalkyl ring; and
'n' ranges between 6 and 28. Typically, the polar organic solvent is at least one selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, dichloromethane and carbon tetrachloride.
Typically, the alkali or alkaline earth metal hydroxide is at least one compound selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)2) and barium hydroxide (Ba(OH)2). Typically, the washing is carried out by using demineralized water.

DETAILED DESCRIPTION:
In one aspect of the present disclosure there is provided a method for treatment of at least partially spent ion-exchange resin to restore its ion-exchange capacity. In the method of the present disclosure inventors have employed a combination of lighter crude oil condensate and polar organic solvent to remove adherences on the spent resin effectively.
The method of the present disclosure is described herein after. Partially spent ion-exchange resin is obtained from a source where highly acidic crude oil is treated with ion-exchange resin for neutralization and desalting. As the ion-exchange resin is obtained after neutralization and desalting of highly acidic crude oil it contains adherences such as asphaltenes, aromatic hydrocarbons, aliphatic hydrocarbons and other resinous material and trapped organic acids. In the first step, the obtained spent ion-exchange resin is contacted with at least one non-acidic crude oil condensate followed by at least one polar organic solvent to obtain partially cleansed ion-exchange resin. The non-acidic lighter crude oil condensate and the polar organic solvent do not interact with acids and salts present in the ion-exchange resin. However, they selectively remove adhered compounds such as asphaltenes, aromatic hydrocarbons, aliphatic hydrocarbons and other resinous material from the spent ion-exchange resin.
The spent ion-exchange resin may be an anion exchange resin. Particularly, the spent ion-exchange resin can be a macro porous anion exchange resin comprising at least one functional group and a resin matrix. The functional group is at least one selected from the group consisting of benzyl trimethyl amine chloride, benzyl dimethyl ethanolamine chloride, tertiary ammonium chloride and quaternary ammonium chloride. The resin matrix of the ion-exchange resin consists of at least one polymer selected from the group consisting of styrene di-vinyl benzene copolymer and polystyrene copolymer.

The inventors of the present invention from the trials found that the method steps of contacting the partially spent resin with non-acidic crude oil condensate and then with polar organic solvent increases the effectiveness of alkaline/alkaline earth solution to remove organic acids.
The inventors of the present disclosure also observed that the non-acidic lighter crude oil condensates having boiling point in the range of 35°C and 370°C are effective in treating the spent ion-exchange resin. The non-acidic lighter crude oil particularly employed is at least one selected from the group consisting of crude oil condensates, light kerosene, toluene, heavy kerosene and diesel. Further, to achieve optimum results the proportion of the spent ion-exchange resin and the non-acidic lighter crude oil condensate is maintained between 1:1 and 1:10.
The polar organic solvent used in treating at least partially spent ion-exchange resin is at least one selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, dichloromethane and carbon tetrachloride. The proportion of the spent ion-exchange resin and the polar organic solvent is maintained between 1: 0.5 and 1: 5 to achieve the desired results.
In one embodiment of the present disclosure the method step of contacting the spent ion-exchange resin with non-acidic crude oil condensate and polar organic solvent is carried out in a column.
In the second step, the partially cleansed ion-exchange resin is treated with at least one alkali or alkaline metal hydroxide solution. In this step, carboxylate anion (RCOO") is freed after exchange with hydroxyl anion (OH") of alkali or alkaline metal hydroxide solution which is then removed by iterative washing with a washing media to obtain a treated ion-exchange resin with restored ion-exchange capacity. The iterative washing is carried out by demineralized water till pH of the media is neutral. The alkali or alkaline metal hydroxide used for treating the partially cleansed ion-exchange resin is at least one selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH),

caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)2) and barium hydroxide (Ba(OH)2).
The organic acid trapped in the ion-exchange resin during neutralization and desalting process of the highly acidic crude oil which is then removed by the process of the present disclosure is at least one compound represented by R(CH2)n COOH, Wherein, R is selected from the group consisting of substituted or un-substituted alkyl group and substituted or un-substituted cycloalkyl ring; and n ranges between 6 and 28.
It would be appreciated by a person skilled in the art that the method step of treating partially cleansed ion-exchange resin with at least one alkali or alkaline metal hydroxide followed by washing with washing media may be carried out at least once after removing adherences using at least one non-acidic crude oil condensate and at least one polar organic solvent.
Further, any or all the method steps of the present disclosure i.e., removing adherences and treating may be repeated at least once to achieve optimum results.
The treated ion exchange resin obtained by using the method of the present disclosure is substantially devoid of adherences and trapped acids.
The ion-exchange resin treated by the method of the present disclosure may be reused for at least 30 times.
The details of the disclosure will further be explained by the way of experiments which do not limit the scope of the disclosure.
Experiment 1:
In this experiment, commercial resin i.e., INDION 810 (Styrene di-vinyl benzene copolymer containing Benzyl trimethyl amine chloride as a functional group) manufactured by Ion Exchange India Ltd, was used to remove acids and salts present

in highly acidic crude oil. The used resin was then treated by a method of the present disclosure and tested for efficiency. The efficiencies of the treated resins were comparatively studied by reusing the treated resins to remove acids and salts present in highly acidic crude oil.
Step 1A: RESIN PACKING
25 ml and 100 ml. of strongly basic macro porous anion exchange resin (INDION 810 manufactured by Ion Exchange India Ltd.) containing quaternary ammonium function group were poured in a glass column with bottom support, separately.
Step IB: RESIN ACTIVATION
5wt% 5 BV aqueous caustic solution was passed through the packed resin at a Liquid hourly space velocity (LHSV) of 1.8/hr. and collected from the bottom. During passage of caustic solution through resin, resin gets activated as the CI" ion of the resin is replaced by active OH" ion. After activation, the resin bed was washed with demineralized water till the pH of the water collected at the bottom of the column is 7 (seven).
Step 1C: REMOVAL OF ACIDS AND SALTS PRESENT IN THE HIGHLY ACIDIC CRUDE OIL
From the top of the neutralized column a highly acidic crude oil was poured with a Liquid Hourly Space Velocity of 1.8/hr. Column temperature was maintained around 50 to 55°C by connecting with hot water circulating bath. The treated crude was collected from the bottom. The exhausted resin bed was slowly purged with N2 to remove traces of crude oils in the resin column.
Analysis of crude oil before and after subjecting to step C is provided in Table 1.
Crude oil before and after resin treatment were subjected to the following analysis:
- TAN by ASTM D 664 method,
- Salt content by ASTM D 3230, and

- Dynamic corrosion test to check the corrosivity of treated HAC oil as well as untreated one.
Table 1:

Sr. No. Analysis of high acidic crude oil before removal of acids and salts Analysis of high acidic crude oil after removal of acids and salts % Reduction

25 ml Bed Crude-1 100 ml Bed
Crude-2 25 ml Bed
Crude-1 100 ml
Bed
Crude-2 25 ml Bed Crude-1 100 ml
Bed
Crude-
2
TAN(mgKOH/gm) 1.49 0.89 0.85 0.45 42.95 49.44
Salt (ptb) 3.7 14.8 1.7 6.8 54.05 54.04
API (°API) 22.93 . 23.32, 22.33 22.35 2.61 4.16
KV (cSt@40°C) 43.05 38.26 51.77 47.51 -20.26 -24.18
Filterable Solid (ptb) 33.8 138 14.8 46 56.21 66.67
CCR(wt%) 4.62 7.61 5.02 7.98 -8.67 -4.86
Asphaltene (wt %) 0.78 6.14 0.74 5.92 5.13 3.58
Cycle 34 7 34 7
Step ID: Restoration of ion exchange capacity of spent resm by only methanol Stage i:
1 BV of methanol was passed through the resin bed obtained in step C to further remove heavier hydrocarbon deposits such as resins and asphaltenes from the resin pores to obtain heavier hydrocarbons free resin. The heavier hydrocarbon free resin was then washed with demineralized water to remove traces of methanol from the resin bed.
Stage ii:
In this stage, resin free of heavier hydrocarbons obtained in Stage i was regenerated as
follows:
The spent resin was packed in a column. 5wt% 5 BV aqueous caustic solution was
passed through the packed resin at a Liquid hourly space velocity (LHSV) of 1.8/hr.
and collected from the bottom. During passage of caustic solution through resin, resin

gets activated as the CI" ion of the resin is replaced by active OH" ion. After activation, the resin bed was washed with demineralized water till the pH of the water collected at the bottom of the column is 7 (seven).
Experiment!:
The spent resin obtained by carrying out steps 1A to 1C of experiment 1 was further
treated as follows:
Step 2D: Restoration of ion exchange capacity of spent resin using only crude oil
Stage i:
5 BV of light non-acidic crude oil condensates (API > 50) was poured with Liquid
Hourly Space Velocity of 1.8/h into the exhausted resin bed obtained in step C.
Passing of light non-acidic crude oil condensates was carried out in a sequence of 30
min flow and 15 min holding to ensure efficient cleaning of the resin bed.
After removing heavier hydrocarbon, the resin bed was washed with 1 BV
demineralized water.
Stage ii:
In this stage, resin free of heavier hydrocarbon obtained in Stage i was regenerated as
follows:
The spent resin was packed in a column. 5wt% 5 BV aqueous caustic solution was
passed through the packed resin at a Liquid hourly space velocity (LHSV) of 1.8/hr.
and collected from the bottom. During passage of caustic solution through resin, resin
gets activated as the .CI" ion of the resin is replaced by active OH ion. After activation,
the resin bed was washed with demineralized water till the pH of the water collected
at the bottom of the column is 7 (seven).
Experiment 3:
The exhausted resin obtained by carrying out steps 1A to 1C of experiment 1 was
further treated as follows:
Step 3D: Restoration of ion exchange capacity of spent resin by non-acidic crude oil condensate followed by methanol

Stage i:
5 BV (125 ml) of light non-acidic crude oil (API > 50) condensates was poured with a flow rate of 45 ml/hr. i.e., Liquid Hourly Space Velocity of 1.8/h into an exhausted resin bed obtained in Step C. Passing of light non-acidic crude oil was carried out in a sequence of 30 min flow and 15 min holding to ensure efficient cleaning of the resin bed. After cleaning by light non-acidic crude oil condensate, 1 BV of methanol was passed through the resin bed to further remove heavier hydrocarbon deposits such as resins and asphaltenes from the resin pores to obtain heavier hydrocarbon free resin. The heavier hydrocarbon free resin was then washed with demineralized water to remove traces of methanol from the resin bed.
Stage ii;
In this stage, resin free of heavier hydrocarbon obtained in Stage i was regenerated as
follows:
The spent resin was packed in a column. 5wt% 5 BV aqueous caustic solution was
passed through the packed resin at a Liquid hourly space velocity (LHSV) of 1.8/hr.
and collected from the bottom. During passage of caustic solution through resin, resin
gets activated as the CI" ion of the resin is replaced by active OH" ion. After activation,
the resin bed was washed with demineralized water till the pH of the water collected
at the bottom of the column is 7 (seven).
The resin obtained was tested for its recyclability by subjecting it iteratively to the
similar process as mentioned in Experiment 1 step C. It was found that resin could be
recycled for 34 times with consistent results. The results of recyclability study are
tabulated in Table 2 herein below. Further, the consistency of resin to process highly
acidic crude oil upto 34 cycles is shown in Figure 1.
Table 2: Average results of recyclability study

Anion Exchange Resin Indion-810
Resin Bed Volume 25 ml
HAC oil used Dalia

LHSV 1.7 h-1
Bed
Temperature 55°C
Bed treating Condition 1 5 wt. % 5 BV aq. caustic SOLN
Solvent Used for Resin Bed Cleaning 5 BV Crude Condensate oil followed by 1 BV MeOH
Average Inlet TAN 1.49 mg KOH / gm
Average Out let TAN 0.86 mg KOH / gm
Average TAN
Reduction 43%
Average Inlet Salt 9.2 ptb
Average Outlet Salt 3.5 ptb
Average Salt Reduction 62%
Average
Volume of Dalia Processed in 1 Cycle 500 ml. (approx. 20BV)
(Breakthrough was considered as outlet TAN = 0.85)
Completed 34 \ (from January to August, 2012)
Total HAC Processed by 25 ml Resin Bed 17.5 It
(700 times of resin
vol.)
The efficiencies of treated resin according to Experiment 1, Experiment 2 and Experiment 3 are depicted in Table 3:

Table 3:

Particulars Efficiency of the resin obtained as per Experiment 1 for trealving HAC oil (Only Methanol) Efficiency of the resin obtained as per Experiment 2 for treating HAC oil ' (Only Condensate oil) Efficiency of the resin obtained as per Experiment 3 for treating HACoil (Condensate oil + Methanol)

100 ml Bed Crude-2 100 ml Bed
Crude-2 100 ml Bed
Crude-2
TAN(mgKOH/gm) 17.95% (decrease) 23.09% (decrease) 49.44 % (decrease)
Salt (ptb) 17.98% (decrease) 28.38% (decrease) 54.04 % (decrease)
API (°API) 2.23% (decrease) 4.23 % (decrease) 4.16 % (decrease)
KV (cSt@40°C) -18.92% (increase) -21.56% (increase) -24.18 % (increase)
Filterable Solid (ptb) 66.1% 66.67 % 66.67 %
CCR(wt%) -2.63% (increase) -4.86 % (increase) -4.86 %
(increase)
Asphaltene (wt %) 3.10%o (decrease) 3.58% (decrease) 3.58 % (decrease)
No. of recycles 1 2 7
Corrosivity of High acidic crude oil (on CS 1010 metal) - - 10 mpy for un treated crude oil 0 mpy with resm treated crude oil
From the above results it can be concluded that the resin treated by the method of the present disclosure i.e., treating with non-acidic crude oil condensate followed by organic polar solvent is more efficient in treating HAC oil.
TECHNICAL ADVANCEMENT AND ECONOMIC SIGNIFICANCE:
Following are the advantages of the method of the present disclosure:
- improved efficiency of treated ion-exchange resin to reduce total acid number of highly acidic crude oil and reduction of restoration cycle shall lead to

processing of more HAC oil which further help to increase gross refining margins (GRM).
- downstream operation related issues are obviated due to absence of naphthenic acid salt in the system.
- cleaning of the resin bed with lighter oil (e.g. condensate) helps to reduce operational cost. Further, the collected crude oil condensate may be mixed with other crude oils for processing.
- the method of the present disclosure not only helps to increase efficiency but also life cycle of the resin.
- salt is reduced along with acidity which helps to reduce desalter load.
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. The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application. The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without

departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

We claim:
1. A method for treatment of at least partially spent ion-exchange resin to restore ion-
exchange capacity, said method comprising the following steps:
a. at least partially removing adherences including asphaltenes, aromatic
hydrocarbons, aliphatic hydrocarbons and other resinous materials from said
spent ion-exchange resin by contacting said ion-exchange resin with at least
one non-acidic crude oil condensate followed by at least one polar organic
solvent to obtain partially cleansed ion-exchange resin; and
b. treating said partially cleansed ion-exchange resin with at least one alkali or
alkaline earth metal hydroxide solution followed by iterative washing to
remove organic acid trapped in said ion-exchange resin to obtain a treated ion-
exchange resin with restored ion exchange capacity.
2. The method as claimed in claim 1, wherein the method steps (a) and (b) are carried out in a column.
3. The method as claimed in claim 1, wherein said method characterized in that the proportion of said spent ion-exchange resin and said non-acidic crude oil condensate ranges between 1:1 and 1:10, and the proportion of said spent ion exchange resin and said polar organic solvent ranges between 1: 0.5 and 1: 5.
4. The method as claimed in claim 1, wherein the non-acidic crude oil condensate is at least one crude oil having boiling point in the range of 35°C and 370°C.
5. The method as claimed in claim 1, wherein the non-acidic crude oil condensate is at least one selected from the group consisting of crude oil condensates, light kerosene, toluene, heavy kerosene and diesel.
6. The method as claimed in claim 1, wherein said spent ion-exchange resin is an anion exchange resin.
7. The method as claimed in claim 1, wherein said spent ion-exchange resin is a macro porous anion exchange resin comprising:

i. at least one functional group selected from the group consisting of benzyl trimethyl amine chloride, benzyl dimethyl ethanolamine chloride, tertiary ammonium chloride and quaternary ammonium chloride; and
ii. a resin matrix containing at least one polymer selected from the group consisting of styrene di-vinyl benzene copolymer and polystyrene co-polymer.
8. The method as claimed in claim 1. wherein said organic acid is at least one
compound represented by R(CH2)n COOH,
Wherein,
R is selected from the group consisting of substituted or un-substituted alkyl
group and substituted or un-substituted cycloalkyl ring; and
n ranges between 6 and 28.
9. The method as claimed in claim 1, wherein said polar organic solvent is at least one
selected from the group consisting of methanol, ethanol, propanol, isopropanol,
butanol, isobutanol, t-butanol, pentanol, dichloromethane and carbon tetrachloride.
10. The method as claimed in claim 1, wherein said alkali or alkaline earth metal
hydroxide is at least one compound selected from the group consisting of lithium
hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium
hydroxide (RbOH), caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)2) and
barium hydroxide (Ba(OH)2).
11. The method as claimed in claim 1, wherein the washing is carried out by using demineralized water.