Ion exchange capacity of zeolite liquid
This invention relates to a method of preparing zeolite materials with enhanced ion exchange capacity and to the zeolite materials obtained thereby as well as their use for the removal of Ca and Mg ions from hard waters. The zeolites modified according to the invention have enhanced ion exchange properties when compared with the parent zeolites.
These properties make them very suitable in all processes involving ion-exchange, particularly in ion exchange capacity of zeolite liquid removal of Ca and Mg ions from hard waters, as discussed below. The framework of a normal zeolite contains tetrahedral Si and Al atoms, the latter being the sites for cations that can be exchanged with others, including protons. This means that the zeolite frameworks are more or less severely damaged by these treatments.
Moreover, there ion exchange capacity of zeolite liquid be recrystallization into other zeolite structures or other species when aluminium-rich zeolites were treated with hot alkali solutions Ion exchange capacity of zeolite liquid fact, only the Al sites with the tetrahedral configuration correspond to the actual cation-exchange sites in a zeolite structure.
The present invention relates to such a method of zeolite modification. Surprising results are obtained ion exchange capacity of zeolite liquid the modification of ZSM-5, Y and X zeolites by treating ion exchange capacity of zeolite liquid zeolites with aqueous solutions of sodium carbonate under mild and severely controlled conditions. Sodium hydroxide is preferably used for adjusting the pH of the alkaline solution to the desired value which ranges from The concentration of the sodium carbonate solution varies from 0.
The amount of NaOH added to adjust the pH of the solution is equivalent to preparing a solution of 0. It is necessary to heat the suspension to 60CC, preferably to 80C. Finally, careful washing the resulting solid with hot water is necessary ion exchange capacity of zeolite liquid remove all the leached species.
In order to show the usefulness of the resulting materials, experiments were carried out in the presence of hard waters containing Ca and Mg ions, in an experimental ion exchange capacity of zeolite liquid which reproduced the conditions existing in a washing machine. The basic procedure for sodium carbonate SC treatment was as follows: The suspension, under moderate stirring, was heated to 80C for 4 h. The suspension was allowed to settle, and the liquid was then rapidly removed.
A fresh volume of sodium carbonate solution was added, and the suspension was again very midly stirred at 80C for a further 4 h. The same procedure might be repeated several times. Then, the suspension was-filtered, and the solid was washed carefully with hot water as follows: A fresh volume of water was added, and the suspension was again ion exchange capacity of zeolite liquid stirred at 80C for a further 3 h. The resulting solid was then dried in an oven at C overnight.
Common Procedures for Characterizinq the zeolites materials: Characterization techniques included the determination of: Tests of removal of Calcium and Maqnesium from hard water: Prior to ion-exchange testing, the zeolites were dehydrated overnight at C. The ion-exchange tests were carried out as follows: The flask was placed in a water bath which was heated at a constant temperature 25C by a hot plate equipped with a magnetic stirrer which ensured a strong and constant stirring action throughout the experiment.
Homogenization of the exchange medium was one of the key factors for the data reproducibility. At that moment, the time was taken as zero. Every minute, a solution sample 2 ml was taken from the flask using a fraction collector, while a reservoir kept adding water to compensate for the volume lost.
The experiment was stopped after 16 min, which corresponds approximately to the residence time of the detergent in the washing machine. The concentrations of Ca and Mg ions remaining in each sample were determined by atomic absorption and finally given in ppm. A polynomial function limited to degree 2, for physically meaningful purposes was used for curve fitting: CCaf was calculated from the curve by replacing t in the previous equation by 16 min.
Magnesium ion removal IRMg was determined in the same way. The total ion removal was expressed as: The rate and the initial rate of magnesium removal rMg and [rMg] were determined in the same way. The invention is illustrated by means of the following non-limiting examples. The total treatment time was 12 h.
ExamPles 4 and 5: Parent zeolites Ion exchange capacity of zeolite liquid and Na-X, powder form were submitted to the ion-exchange testing in the presence of the hard water, as previously described.
The computed results of such tests are reported in Table 2. Examples 6 and 7: The result is reported in Table 2. The average size of micropores decreases slightly, indicating that the Si removal is followed by some sort of "healing" process which results in slightly narrower zeolite micropores.
This means that the ion-exchange capacity of the zeolite increases with such a treatment. However, sodium hydroxide present in the treatment suspension in relatively small amounts, provides the minimum of basicity which is required to start the selective Si removal. The more siliceous the zeolite, the lower the amount of NaOH required for such an initiation phase, and then, the easier the Si removal.
However, if a too great alkalinity is used for the treatment, the zeolite structure may undergo a partial, and even a total, collapse which results in more or less amorphous materials with no commercial use. This is due to its narrow pore size 0. In fact, Mg is known to form complex ions with water -molecules by solvatation. Moreover, the initial rates of Ca and Mg removal are higher than those of the commercial Na-A. Bisio, Butterworths, Guilford,p. Le Van Mao, N. Denes, 9th Ion exchange capacity of zeolite liquid Zeolite Conference, J.
Ion exchange capacity of zeolite liquid Van Mao, J. Nastro, 9th International Zeolite Conference, J. Goeke, 9th International Zeolite Conference, J.
Goeke, Zeolites, 12, In accordance with the present invention, there are now provided zeolite materials with enhanced ion exchange capacity, which are obtained by treating ZSM-5, Y and X zeolites with aqueous solutions of sodium carbonate and sodium hydroxide.
With such a treatment, some silicon species are selectively removed from the zeolite frameworks, thus increasing the density of the tetrahedral Al sites.
The invention concerns also the use of the thus obtained zeolites for the removal of Ca and Mg ions from hard waters. Guisnet, Zeolites, 10, Method according to claim 1, wherein the pH of the sodium carbonate solution is adjusted by adding sodium hydroxide thereto. ZSM-5, Y and X zeolites having enhanced ion exchange capacity, produced by the method of any one of claims 1 to 7.
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