Regeneration Of Carboxylic Acrylic Cationexchange Resins By Stochiometric Amount
REGENERATION of CARBOXYLIC ACRYLIC CATION‑EXCHANGE RESINS by STOCHIOMETRIC AMOUNT
of a SULFURIC ACID
A.V. Mamchenko, T.I. Yakymova, G.V. Klimova
Institute of Colloid Chemistry and Chemistry of Water, Ukrainian National Academy of Sciences, Vernadsky avenue 42, 03680 Kyiv, Ukraine
The features of carboxylic acrylic cation-exchange resins are their high total exchange capacity, it accounts for 3800 – 4500 mol/m3, and the opportunity of regeneration by stochiometric amount of an acid, including one being in wastes, for example, in the wastewater of H-filters of water desalination plants.
One of the primary factors determining the opportunity of realization of specified powerful advantages of acrylic cation-exchange resins in comparison with sulfonic cation-exchange resin KY-2-8, traditionally used in Ukraine for water softening, is the residual contents of an absorbed from water calcium, magnesium and sodium ions in a ionite phase after sorbent regeneration by stochiometric amount of an acid. It is known, that at regeneration of carboxylic acrylic cation-exchange resins in the standard water-treatment equipment in one stage by the stochiometric amount of a sulfuric acid 20 – 30 % of total exchange capacity of sorbent is lost unproductively, owing to the high residual contents of desorbed ions in regenerated form of resin.
The optimization of a mode of operation of ion-exchange filters, including one due to decrease of a part of ions which have been not desorbed, is possible on the basis of the theory of nonequilibrium sorption dynamics.
For the analysis of process of regeneration of the carboxylic acrylic cation-exchange resin Lewatit CNP 80, exhausted at water softening, by solution of a sulfuric acid in coflow and counterflow modes and in mode of suspended bed of the ionite, the theoretical model of dynamics of one component sorption intraparticle diffusion in a fixed bed of an ionite was used.
The application of the simplified model of process has appeared possible owing to low sorption selectivity of sodium ions and close sorption selectivities of calcium and magnesium ions by cation-exchange resin.
The solution of the system of differential equations of theoretical model of dynamics of one component sorption intraparticle diffusion is given by
t = aox(vCo)-1 –b*-1 {(BCo)-1ln[(Co/ С*) - 1] + ln(1 - С*/Co) + 1} (1)
where t – time counted from the moment of a beginning of process; ao – specific magnitude of sorption calculated per unit of bed volume ; x – distance from an input of a liquid in a sorbent bed; v – linear rate of a liquid flow calculated on complete section of a sorption column; Co – sorbate concentration in an initial solution; b* – kinetic coefficient of intraparticle mass transfer; С* – sorbate concentration in a liquid phase in a sorbent bed on distance x from an input of a flow in a column at the moment of time t; B – constant of the equation of component sorption equilibrium which has been written as
a = A С*/(1 + B С*) (2)
where a – specific magnitude of component sorption, calculated per unit of sorbent volume at equilibrium concentration С*; А – constant.
It is shown, that the simplified model describes the process of sorbent regeneration adequately irrespective of a way of its organization and allows to carry out a priori estimations of changes of its characteristics at a variation of linear rate of a feeding of regeneration solution .
The value of effective kinetic coefficient b* was found, knowledge of which allows to determine all main technical characteristics of process of regeneration at a variation of conditions of cation-exchange resin operation, including realization of regeneration on two portions scheme with use wastewater of H‑filters of the first stage of water desalination plants.
It was established, that the mode of realization of process of regeneration has an effect only on a value of effective kinetic coefficient, which at both a countercurrent mode and ion-exchange resin regeneration in the mode of suspended bed is empirical adjusting parameter, which magnitude, nevertheless, does not depend on linear rate of a regeneration solution feeding.
It is given solution of a task of optimization of cation-exchange resin regeneration by stochiometric amount of a sulfuric acid, which is included in composition of wastes.
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