Determination of the total dynamic exchange capacity of the cation exchanger. Ion exchange
Goal of the work- to determine one of the main physical and chemical characteristics of the ion exchanger - the total dynamic exchange capacity (PDEC).
Essence of work. The maximum amount of ions that an ion exchanger can absorb determines its total exchange capacity. It corresponds to the concentration of ionogenic groups. The capacity is expressed as the number of millimol equivalents of the exchanged ion per 1 g of dry (mmol equiv/g) or 1 ml of swollen ion exchanger (mmol equiv/ml) at pH values corresponding to its full ionization. Determination of the capacity of ion exchangers is carried out in static or dynamic conditions (in an ion-exchange column).
The capacity of ion exchangers under dynamic conditions is determined from the output curves constructed in the coordinates "Concentration of the exchanged ion at the outlet of the column - eluate volume". They are used to find the full dynamic exchange capacity (PDOE) and the dynamic exchange capacity to breakthrough (DOE), which shows the amount of absorbed ions until they appear in the eluate (breakthrough).
In laboratory work, it is necessary to determine the PDOE of the strongly acidic cation exchanger KU-2 for copper (II). To do this, a solution of CuSO 4 continuously pass through a column filled with KU-2 cation exchanger in H + -form, and separate portions of the outflowing solution are collected ( eluate) into volumetric flasks for the subsequent determination of the concentration of Cu 2+ in each of them.
When a CuSO 4 solution is passed through the ion exchanger layer, the ion exchange reaction proceeds:
2 R–SO 3 H + CuSO 4 Û (R–SO 3) 2 Cu + H 2 SO 4.
In the first portions of the eluate, Cu 2+ ions should be absent, since the ion exchanger layer will gradually become saturated with these ions as the solution passes through. Then comes slip Cu 2+ ions into the eluate, after which the Cu 2+ concentration at the column outlet will increase until it equals the Cu 2+ concentration at the column inlet, which indicates full saturation ionite layer.
Analysis of the eluate for the content of Cu 2+ ions is carried out photometrically. The definition is based on the formation of copper (II) ammonia, which has an intense blue color:
Cu 2+ + 4NH 3 ↔ 2+.
The light absorption maximum of this compound corresponds to λ = 620 nm. The calibration curve method is used to find the unknown concentration.
Equipment, utensils, reagents: column with KU-2 sulfocationite in hydrogen form; photoelectric colorimeter; cuvettes ( l= 3 cm); a Mariotte flask for uniform supply of the solution to the column; glasses; volumetric flasks with a capacity of 25.0 ml (3 pcs.) and 50.0 ml (6 pcs.); graduated pipettes; measuring cylinder with a capacity of 25 ml, 0.1 N. standard solution CuSO 4 ; 3 n. HCl solution; reagents for the detection of Cu 2+ ; 5% aqueous NH 3 solution; universal indicator paper.
Completing of the work
1. Preparing the ion exchanger for work. In the work, a pre-prepared column with cation exchanger is used, the weight of which must be clarified with the teacher.
First of all, it is necessary to convert the cation exchanger into the hydrogen form. To do this, 80–100 ml of 3N hydrochloric acid are passed through the column. HCl solution, checking the filtrate for the content of Cu (II). As analytical reagents for the detection of copper (II), you can use a solution of NaOH or KOH ( a blue precipitate is formed Cu (OH) 2), an aqueous solution of NH 3 ( an ammonia complex of copper (II) is formed intensively of blue color ) and etc.
In the absence of Cu (II) cations in the filtrate, the cation exchanger in the column is washed with distilled water until neutral. In this form, the ion exchanger is considered prepared for work.
2. Carrying out ion exchange under dynamic conditions. A solution of CuSO 4 is poured into a Mariotte flask attached to the top of the column. Then they begin to pass it through a layer of cationite, maintaining a constant (~ 1 ml/min) filtration rate and adjusting it at the outlet with a screw clamp. When performing work, it is necessary to ensure that the level of the solution in the column is maintained constant. The filtrate is collected in separate portions in volumetric flasks with a capacity of 25.0 ml, and in each of them the concentration of Cu (II) is determined ( see below).
The passage of the CuSO 4 solution through the cation exchanger is stopped when the content of the saturating Cu (II) ion in the last two samples remains constant.
3. Conducting an analysis.
§ Construction of a calibration graph. Aliquots of standard 0.1 N. CuSO 4 solution (1.00; 2.50; 4.00; 5.00; 6.00 ml) is placed in volumetric flasks with a capacity of 50.0 ml, 25 ml of 5% ammonia solution and distilled water are added to each flask up to the mark. In a volumetric flask of the same capacity, prepare a reference solution containing 25 ml of ammonia solution.
Measure light absorption ( A) one of the prepared solutions in a cuvette with a layer thickness of 3 cm with all filters and according to the dependence A = f(λ) carry out the choice of filter.
Then measure the light absorption of all reference solutions with the selected light filter. The measurement results are processed by the least squares method, preferably using a PC, and a calibration graph is built in the coordinates A – WITH, mmol equiv/ml.
§ Filtrate analysis. Each collected portion of the eluate (25.0 ml) was quantitatively transferred into a volumetric flask with a capacity of 50.0 ml and diluted to the mark with 5% ammonia solution. The light absorption is measured in relation to the reference solution and the concentration of Cu (II) in the solution is found from the calibration curve.
If the measured value A≥ 0.6, then an aliquot of this solution (10.0 ml) is placed in a volumetric flask with a capacity of 50.0 ml, 20 ml of a 5% NH 4 OH solution is added and diluted with distilled water to the mark. The resulting solution is photometered. When calculating the concentration of copper (II) in each portion of the eluate, it is necessary to take into account the dilution carried out.
4. Processing of received data.
4.1. Calculation of PDOE:
by the measured value of light absorption ( A) each of the solutions determine the concentration of Cu (II) ions using a calibration graph;
· according to the law of equivalents, the concentration of Cu (II) ions is calculated in all portions of the eluate (25 ml), taking into account all previously made dilutions;
Calculate the chemical amount of Cu (II) ions (mmol equiv) in the total volume missed solution according to the formula
Where V(Cu 2+) = 25 ml - the volume of one portion of the eluate; p- the number of servings.
Calculate the chemical amount of Cu (II) ions (mmol equiv) in all portions of the eluate according to the formula
Where C i(1/2 Cu 2+) - concentration of copper in i-th portion of the eluate.
By difference, find the number of mmol equivalents of Cu (II) absorbed by the ion exchanger:
value of dynamic exchange capacity ion exchanger (PDOE) is calculated by the formula
In some cases, at the instruction of the teacher, in addition, DOE is calculated.
4.2. Building an output curve. Based on the data obtained, an output curve is built, plotting the volume of eluate (ml) from the beginning of the experiment on the abscissa axis, and the concentration of copper (II) in each portion of the eluate (mmol equiv/l) along the ordinate axis.
6. The limitation of the validity period was removed according to protocol N 5-94 of the Interstate Council for Standardization, Metrology and Certification (IUS 11-12-94)
7. EDITION (January 2002) as amended (IUS 3-91)
This standard applies to ion exchangers and specifies methods for determining the dynamic exchange capacity with complete regeneration of the ion exchanger and with a given flow rate of the regenerating agent.
The methods consist in determining the amount of ions absorbed from the working solution by a unit volume of the swollen ion exchanger during the continuous flow of the solution through the ion exchanger layer.
1. SAMPLING METHOD
1. SAMPLING METHOD
1.1. The sampling method is indicated in the regulatory and technical documentation for specific products.
1.2. For ion exchangers, in which the mass fraction of moisture is less than 30%, a sample (100 ± 10) g is taken. For swelling, the sample is placed in a glass with a capacity of 600 cm 3 and poured with a saturated solution of sodium chloride, which should cover the ion exchanger layer in excess, taking into account its swelling. After 5 hours, the ion exchanger is washed with distilled water.
1.3. For ion exchangers with mass fraction more than 30% moisture, a sample (150 ± 10) g is taken into a glass with a capacity of 600 cm 3 and 200 cm 3 of distilled water are poured.
2. REAGENTS, SOLUTIONS, WAREHOUSES, INSTRUMENTS
Distilled water in accordance with GOST 6709 or demineralized water that meets the requirements of GOST 6709.
Barium chloride according to GOST 742, chemically pure, solution with a mass fraction of 10%.
Calcium chloride 2-aqueous, chemically pure, solutions of concentrations (СаСl=0.01 mol/dm (0.01 N) and (СаСl)=0.0035 mol/dm (0.0035 N).
Hydrochloric acid according to GOST 3118, chemically pure, solutions with a mass fraction of 5% and concentrations (HCl) = 0.5 mol / dm (0.5 N), (HCl) = 0.1 mol / dm (0.1 N) and (HCl) = 0.0035 mol / dm (0.0035 N).
Sulfuric acid according to GOST 4204, chemically pure, solutions with a mass fraction of 1%, concentration (HSO) = 0.5 mol / dm (0.5 N).
Sodium hydroxide according to GOST 4328, chemically pure, solutions with a mass fraction of 2, 4, 5%, concentrations (NaOH)=0.5 mol/dm (0.5 N), (NaOH)=0.1 mol/dm (0.1 N), (NaOH)=0.0035 mol/dm (0.0035 N).
Sodium chloride according to GOST 4233, chemically pure, saturated solution and concentration solution (NaCI)=0.01 mol/dm (0.01 N).
A mixed indicator, consisting of methyl red and methylene blue or methyl red and bromcresol green, is prepared according to GOST 4919.1.
Indicator methyl orange or methyl red, a solution with a mass fraction of 0.1%, is prepared according to GOST 4919.1.
Indicator phenolphthalein, an alcohol solution with a mass fraction of 1%, is prepared according to GOST 4919.1.
Chemical lime absorber KhPI-1 according to GOST 6755 or soda lime.
Tube (calcium chloride) according to GOST 25336.
Beaker 1000 according to GOST 1770.
Cylinders in accordance with GOST 1770 versions 1-4 with a capacity of 100 and 250 cm3 and versions 1, 2 with a capacity of 500 and 1000 cm3.
Glasses B or H according to GOST 25336 in any design with a capacity of 600 and 1000 cm.
Flasks Kn-1-250 according to GOST 25336.
Pipettes 2-2-100, 2-2-25, 2-2-20 and 2-2-10 according to NTD.
Burettes according to NTD types 1, 2, versions 1-5, accuracy classes 1, 2, with a capacity of 25 or 50 cm3, with a division value of not more than 0.1 cm3 and burettes of types 1, 2, execution 6, accuracy classes 1, 2, with a capacity of 2 or 5 cm3, with a division value of not more than 0.02 cm3.
Volumetric flasks of executions 1, 2 in accordance with GOST 1770, accuracy classes 1, 2, with a capacity of 10, 25 and 100 cm3.
Sieve with a control grid 0315K according to GOST 6613 with a shell with a diameter of 200 mm.
Cup ChKTs-5000 in accordance with GOST 25336 or made of polymerization material, sufficient to place a sieve into it.
The laboratory installation (see the drawing) consists of a bottle 1 and a glass column 6 with an internal diameter of (25.0 ± 1.0) mm and a height of at least 600 mm to determine the dynamic exchange capacity under conditions of complete regeneration of the ion exchanger and an internal diameter of (16.0 ± 0.5) mm and a height of at least 850 mm for determination under conditions of a given flow rate of the regenerating substance. A type 7 FKP POR 250 XC filter according to GOST 25336 or another filtering device resistant to acids and alkalis, impermeable to ion exchanger grains larger than 0.25 mm and having low filtration resistance, is soldered into the lower part of the column. The column is connected to the bottle using a glass tube 3 and a rubber hose 4 with a screw clamp 5. To prevent the ingress of carbon dioxide from the air into the sodium hydroxide solution, a calcium chloride tube 2 with an absorber KhPI-1 is installed in the cork of the bottle.
Laboratory setup
It is allowed to use other measuring instruments with metrological characteristics not worse than those indicated, as well as reagents in quality not lower than those indicated.
3. METHOD FOR DETERMINING THE DYNAMIC EXCHANGE CAPACITY WITH COMPLETE REGENERATION OF THE IONITE
3.1. Preparing for the test
3.1.1. Preparation for testing is carried out according to GOST 10896 and after preparation, the ion exchanger is stored in a closed flask under a layer of distilled water.
Cation exchange resin grade KU-2-8chS and anion exchange resin grade AV-17-8chS are not prepared for testing according to GOST 10896.
3.1.2. An ion exchanger sample from the flask in the form of an aqueous suspension is transferred to a cylinder with a capacity of 100 cm 3 and the ion exchanger layer is compacted by tapping on the hard surface of the bottom of the cylinder until shrinkage stops. The volume of the ion exchanger is adjusted to 100 cm 3 and the ion exchanger is transferred into the column with the help of distilled water, making sure that no air bubbles get between the granules of the ion exchanger. Excess water is drained from the column, leaving a layer 1-2 cm high above the level of the ion exchanger.
3.1.3. The ion exchanger in the column is washed with distilled water, passing it from top to bottom at a rate of 1.0 dm/h. In this case, the anion exchanger is washed from alkali (by phenolphthalein), and the cation exchanger from acid (by methyl orange).
3.1.4. Strong base anion resins in the hydroxyl form are quickly charged and washed with carbon dioxide-free water.
3.2. Conducting a test
3.2.1. Determination of the dynamic exchange capacity of ion exchangers consists of several cycles, each of which includes three successive operations - saturation, regeneration, washing, the conditions for which are given in table.1.
Table 1
Conditions for determining the dynamic exchange capacity with complete regeneration of the ion exchanger
Index | Ionite class | Working solution for saturation of ion exchangers | Saturation control | Regenerating | |||
saturate | wash- | regene- |
|||||
Dynamic exchange capacity before breakthrough () | Strongly- | Calcium chloride (CaCl)=0.01 mol/dm (0.01 N) | Up to the concentration of calcium ions in the filtrate (Ca)=0.05 mmol/dm (0.05 mg eq/dm) is determined according to GOST 4151 | Hydrochloric acid, solution with a mass fraction of 5% | |||
Strongly- | Sodium chloride (NaCl)=0.01 mol/dm (0.01 N) | Until the alkali concentration decreases by 0.5 mmol / dm (0.5 mg equiv / dm) in comparison with its maximum stable value in the filtrate [mixed indicator, titrating solution, hydrochloric acid concentration (HCl) = 0.01 mol / dm (0.01 N)] and until the content of chlorine ions increases in comparison with its stable content in the filtrate (determined according to GOST 15615) | Sodium hydroxide, solution with a mass fraction of 5% | ||||
Weak- | Until acid appears in the filtrate (by methyl orange) | ||||||
Full dynamic exchange capacity () | Weak- | Hydrochloric acid (HCl)=0.1 mol/dm (0.1 N) | Before equalizing the concentration of the filtrate with the concentration of the working solution | Sodium hydroxide, solution with a mass fraction of 2% | |||
Notes:
1. When determining the concentration of Ca ions according to GOST 4151
2. Specific load is the volume of the solution passed through the volume of the ion exchanger in 1 hour. For example, 5 dm / dm h corresponds to the filtration rate at which 500 cm of the solution (8.3 cm / min) passes through 100 cm of the ion exchanger in 1 hour.
3. The filtration rate is set by measuring in a measuring cylinder the volume of the filtrate obtained over a certain time interval.
Solutions and water are fed from top to bottom. When the anion exchanger of grades AN-1 and AN-2FN is saturated, the solutions are fed from bottom to top.
3.2.2 Before carrying out the saturation, regeneration and washing operations, the column is filled with the appropriate solution. The solution layer above the ion exchanger should be (15 ± 3) cm.
3.2.3. After saturation, regeneration, and washing, a liquid layer 1–2 cm high is left in the column above the ion exchanger.
3.2.4. The column with an ion exchanger is filled with a working solution for a specific class of ion exchanger (see Table 1) so that the solution layer above the ion exchanger is (15±3) cm, and the appropriate filtration rate is selected.
When working solutions with a concentration of 0.1 mol / dm (0.1 N) are passed through a column with an ion exchanger, the filtrate is collected in cylinders with a capacity of 250 cm3, at a concentration of 0.01 mol / dm (0.01 N) - in cylinders with a capacity of 1000 cm3. and 250 cm3, respectively, to the concentrations of the working solution.
3.2.5. A sample is taken from each portion of the filtrate and saturation is controlled in accordance with Table 1.
3.2.6. After the ions of the working solution appear in a portion of the filtrate, the total volume of the filtrate is calculated.
3.2.7. To determine the total dynamic exchange capacity, the solution is continued to pass until the concentration of the filtrate equalizes with the concentration of the working solution. Saturation control in this case is carried out by titrating the sample with an acid solution (sodium hydroxide) with a mixed indicator until the color changes.
3.2.8. Before regeneration, the ion exchanger in the column is loosened by a stream of distilled water from the bottom up so that all the grains of the ion exchanger are in motion. Loosening of the KU-1 cation exchanger and the AN-1 and AN-2FN anion exchangers is carried out before the saturation operation.
3.2.9. The regeneration of the ion exchanger is carried out with an acid solution (sodium hydroxide) at the rate indicated in Table 1. The filtrate is continuously collected in portions with a cylinder of 250-1000 cm 3, adding 3-4 drops of the indicator. When an acid (sodium hydroxide) appears in the filtrate, its concentration is determined in subsequent portions. To control the filtrate, a sample is taken with a pipette or a volumetric flask and titrated with an acid solution (sodium hydroxide) of concentration (HCl, HSO) = 0.5 mol / dm (0.5 N), (NaOH) = 0.5 mol / dm (0.5 N) in the presence of an indicator
3.2.10. The acid solution (sodium hydroxide) is passed until the concentration of the filtrate is equal to the concentration of the regenerating solution.
3.2.11. After regeneration, the ion exchanger is washed with distilled water until neutral in terms of methyl orange (phenolphthalein) at the rate indicated in Table 1. Then the ion exchanger is kept in distilled water for 1 hour and the filtrate is checked again. If the filtrate is not neutral, the resin is washed again.
3.2.12. The determination of the dynamic exchange capacity is completed if in the last two cycles the results are obtained, the discrepancy between which does not exceed 5% of the average result.
3.2.13. The dynamic exchange capacity of the anion exchange resin AV-17-8chS is determined on two parallel samples in the first saturation cycle, before the appearance of ions of the working solution in the filtrate. The filtrate is collected in portions of 250 cm3. The result is taken as the arithmetic mean of the results of two determinations, the allowable discrepancy between which does not exceed 5% of the average result.
(Amendment, IUS 3-91).
4. METHOD FOR DETERMINING THE DYNAMIC EXCHANGE CAPACITY WITH A GIVEN CONSUMPTION OF THE REGENERATING SUBSTANCE
4.1. Preparing for the test
4.1.1. The ionite, selected in accordance with paragraphs 1.2 and 1.3, is separated from fine fractions by wet sieving according to GOST 10900 using a sieve with a mesh N 0315K.
4.1.2. The screened anion exchange resin is placed in a beaker, 500 ml of sodium hydroxide solution with a mass fraction of 4% is added and mixed. After 4 hours, the hydroxide solution is drained, and the anion exchanger is washed with water until a slightly alkaline reaction with respect to phenolphthalein and transferred to a column, as indicated in paragraph 3.1.2.
4.1.3. The screened cation exchanger is washed from suspension and turbidity with distilled water by decantation until clear wash water appears and transferred to the column in accordance with clause 3.1.2.
4.2. Conducting a test
4.2.1. Determination of the dynamic exchange capacity of ion exchangers before the appearance of ions of the working solution in the filtrate () consists of several cycles, each of which includes three successive operations - saturation, regeneration, washing, the conditions for which are given in table 2. Solutions and water are fed from top to bottom. The height of the liquid layer above the level of the ion exchanger is set as indicated in paragraphs 3.2.2 and 3.2.3.
table 2
Conditions for determining the dynamic exchange capacity of ion exchangers at a given flow rate of the regenerating agent
Ionite class | Regenerating | The rate of specific consumption of regen- | Wash control | Working solution for saturation of the ion exchanger | Saturation control | Filtration speed |
||
nasy- | laundering | reg- |
||||||
Strongly | Up to a residual acid concentration in the filtrate, not more than | Calcium chloride (СаСl=0.0035 mol/dm (0.0035 N) | Up to the concentration of calcium ions in the filtrate more than (Ca)=0.05 mmol/dm | |||||
Weak- | Sulfuric acid, solution with a mass fraction of 1% | Until the absence of sulfate ions in the filtrate (sample with BaCl in the presence of HCl) | Sodium hydroxide (NaOH)=0.0035 mol/dm (0.0035 N) | Up to the concentration in the filtrate of sodium hydroxide (NaOH)=0.1 mmol/dm | ||||
Strongly- | Sodium hydroxide with a mass fraction of 4% | Up to a residual concentration of sodium hydroxide in the filtrate, not more than (NaOH)=0.2 mmol/dm | Sodium chloride (NaCI)=0.01 mol/dm (0.01 N) | Until the alkali concentration decreases by (NaOH)=0.7 mmol/dm | ||||
Weak- | Sodium hydroxide, solution with a mass fraction of 4% | Up to a residual concentration of sodium hydroxide in the filtrate, not more than (NaOH) = 0.2 mmol / dm (0.2 mg eq / dm) for phenolphthalein | Hydrochloric (sulfuric) acid (HCl, HSO) \u003d 0.0035 mol / dm (0.0035 N.) | Up to a residual acid concentration in the filtrate no more than (N)=0.1 mmol/dm (0.1 mg equiv/dm), the indicator is mixed, the titrating solution is sodium hydroxide concentration (NaOH)=0.01 mol/dm (0.01 N.) | ||||
Notes:
1. When expressing the rate of specific consumption of the regenerating substance () in grams per mol, the word "mol" means the molar mass of the ion equivalent (Na, K, Ca, Mg, Cl, NO, HCO, HSO, CO, SO
Etc.).
2. The actual consumption of the regenerating agent should not differ from the specified rate by more than 5%.
3. When determining the concentration of Ca ions according to GOST 4151, it is allowed to use 2-3 drops of a chrome-dark blue indicator and titrate with a solution of Trilon B concentration (NaHCON 2HO) = 0.01 mol / dm (0.01
4. Specific load is the volume of the solution passed through the volume of the ion exchanger in 1 hour. For example, 5 dm / dm h corresponds to the filtration rate at which 500 cm of the solution (8.3 cm / min) passes through 100 cm of the ion exchanger in 1 hour.
5. The filtration rate is set by measuring in a measuring cylinder the volume of the filtrate obtained over a certain time interval.
In order to avoid gypsuming of the cation exchanger, regeneration with acid and washing from regeneration products is carried out without interruption, avoiding a gap between operations.
Before carrying out each subsequent cycle, the ion exchanger is loosened by a flow of water from the bottom up so that all the grains of the ion exchanger are in motion.
4.2.2. A regenerating solution is passed through the ion exchanger in the column, the volume of which () in cubic centimeters is calculated by the formula
where is the specified rate of specific consumption of the regenerating substance, g/mol (g/g eq);
- dynamic exchange capacity; choose according to the regulatory and technical documentation for a specific ion exchanger, mol / m (g eq / m); for ion exchangers of grades AV-17-8, AN-31 and EDE-10P, an increased value of dynamic exchange capacity up to 3 is allowed for the first regeneration;
is the volume of the ion exchanger sample, cm;
- concentration of the regenerating solution, g/dm.
The amount of regenerating solution is measured at the outlet of the column with a cylinder or beaker. Then the column is disconnected, the level of the solution above the ion exchanger in the column is lowered to 1–2 cm, and the bottom cap is closed.
4.2.3. After regeneration, the ion exchangers are washed with distilled water to remove excess acid (sodium hydroxide) at the rate indicated in Table 2.
Periodically take a sample of the filtrate and titrate with solutions of sodium hydroxide (acid) concentration (NaOH, HCl, HSO)=0.1 mol/dm (0.1 N) in the presence of methyl orange (phenolphthalein).
Washing control according to table.2.
4.2.4. After washing, the column is filled with a working solution and the saturation rate is set according to Table 2.
When working solutions of concentration 0.01 mol/dm (0.01 N) are passed through the column, the filtrate is collected in a cylinder with a capacity of 250 ml; at a concentration of 0.0035 mol/dm (0.0035 N), a cylinder with a capacity of 1000 ml is used. 0 cm according to the concentrations of the working solution.
4.2.5. To control saturation, a sample is taken from a portion of the filtrate and analyzed in accordance with Table 2. If the result of the analysis shows that the saturation level has not reached the values indicated in Table 2, all previous samples of the filtrate may not be analyzed.
4.2.6. After the ions of the working solution appear in a portion of the filtrate in the amounts indicated in Table 2, the saturation is completed and the total volume of the filtrate () and the dynamic exchange capacity are calculated.
4.2.7. The ion exchanger is subjected to the second regeneration and washed in accordance with paragraphs 4.2.2 and 4.2.3.
When calculating the regenerating agent required for the second cycle, use the value of the dynamic exchange capacity obtained in the first cycle in accordance with paragraph 4.2.6.
Before carrying out subsequent cycles of saturation, the consumption of the regenerating substance is calculated from the value of the dynamic exchange capacity obtained in the previous cycle.
4.2.8. The determination is completed if in the last two cycles the results are obtained, the allowable discrepancies between which do not exceed 5% of the average result, with the actual specific consumption of the regenerating substance that differs from the given norm by no more than 5%.
5. PROCESSING THE RESULTS
5.1. Dynamic exchange capacity () in moles per cubic meter(g Eq/m) before the appearance of ions of the working solution in the filtrate is calculated by the formula
where is the total volume of the filtrate passed through the ion exchanger until the ions of the working solution appear, cm;
- the volume of the ion exchanger, see
5.2. The actual consumption of the regenerating substance () in grams per mole (g / g eq) of absorbed ions is calculated by the formula
where is the volume of the regenerating solution, cm;
- concentration of the regenerating solution, g/dm;
- the total volume of the filtrate passed through the ion exchanger before the appearance of ions of the working solution, cm;
- concentration of the working solution, mol / dm (n.
5.3. The total dynamic exchange capacity () in moles per cubic meter (g eq / m) is calculated by the formula
where is the total volume of the filtrate passed through the ion exchanger before equalizing the concentrations of the filtrate and the working solution, cm;
- concentration of the working solution, mol / dm (n.);
- the volume of the portion of the filtrate after the appearance of ions of the working solution (breakthrough), cm;
- concentration of the solution in a portion of the filtrate after the appearance of ions of the working solution (breakthrough), mol / dm (n.);
- the volume of the ion exchanger,
5.4. The arithmetic mean of the results of the last two cycles is taken as the result of the determination, the allowable discrepancies between which do not exceed ± 5%, with a confidence probability = 0.95.
Note. When expressing the dynamic exchange capacity of ion exchangers in moles per cubic meter, the word "mol" refers to the molar mass of the ion equivalent (Na, K, Ca, Mg, Cl, NO, HCO, HSO, CO, SO, etc.).
The text of the document is verified by:
official publication
Ionites. Methods of determination
exchange capacity: Sat. GOSTs. -
Moscow: IPK Standards Publishing House, 2002
Page 3
A high ion exchange rate makes it possible to use filter layers of a very small height (5–25 mm) and achieve the use of 50–90% of the total exchange capacity of ion exchangers instead of 20–50% used in conventional bulk filters with the usual fractional composition of ion exchangers in filter layers of great height (above 900 mm), provided that a filtrate of equivalent quality is obtained.
The titration curves obtained using the potentiometric method make it possible to give the main chemical characteristic of the ion exchanger: the presence of active groups and the degree of their dissociation depending on the pH of the medium, the total exchange capacity of the ion exchanger, determined by the sum of all active groups that make up the ion exchanger and enter into the reaction, the exchange capacity for individual active groups, the exchange capacity of ion exchangers at a constant pH value of the medium, and also allows you to determine what type of ion exchanger is acidic or basic. Titration curves are obtained at a constant salt concentration, since the exchange capacity of the ion exchanger depends on the pH of the medium and the concentration of the exchanged ion in the solution.
The alternation of ion exchange with reduction or precipitation reactions in order to convert substances adsorbed on ion exchangers into a non-dissociated and insoluble form makes it possible to concentrate in total such an amount of adsorbed substance that is 10–15 times higher than the total exchange capacity of the ion exchanger. This is especially indicative when noble metals are concentrated on ion exchangers, whose ions are easily reduced to metal and in this form settle on ion exchangers.
Exchange capacity is a measure of an ion exchanger's ability to absorb ions from a solution. The total exchange capacity of the ion exchanger (POE) is determined by the maximum number of milligram equivalents of ions that can be absorbed by 1 g of air-dry ion exchanger. So, for example, in the KU-2 cation exchanger, the POE value is about.
Depending on the conditions of determination, there are full (POE), static (COE) and dynamic (working) exchange capacity (DOE, ROE) of the ion exchanger. The total exchange capacity of the ion exchanger is characterized by total number active groups of the ion exchanger per unit volume of the resin.
The efficiency of using the ion-exchange dynamic method for cleaning solutions is ensured mainly by the use of high-capacity ion exchangers. Since the full exchange capacity of ion exchangers under dynamic conditions, as is known, is realized incompletely, when choosing optimal conditions In carrying out the process, the task is to reduce the difference between the total exchange capacity of the column and the capacity of the column before the breakthrough of ions into the filtrate. On the other hand, it is almost equally important to choose an ion exchanger, because under given kinetic conditions, the slope of the front of the ion that appears first in the filtrate is determined, among other things, by the nature of this ion. For the purposes of purification of solutions, therefore, one should choose ion exchangers characterized not only by a high exchange capacity, but also great value exchange constants of the least sorbed ion. The qualitative composition for the choice of the ion exchanger does not matter, since one of the features of the mixture exchange dynamics is that the slope of the front of the less sorbed ion does not depend on the properties of other components of the mixture. These provisions determine the expediency of using for the purpose of desalting solutions of ion exchangers with a large number of cross-links and make it undesirable to use weakly acidic ion exchangers in the hydrogen form.
The capacity of the ion exchanger is expressed in milliequivalents (meq. When determining the total exchange capacity of the ion exchanger, the content of all exchangeable groups in it is determined. To do this, use small columns, for example, centrifuge columns of the type shown in Fig. 5.7, or funnels with paper filters.
In accordance with the Donnan principle of electroneutrality within a grain, the maximum amount of exchangeable counterions is determined by the number of ionogenic groups introduced into the matrix. Therefore, the total exchange capacity of the ion exchanger can theoretically be calculated based on the equivalent weight of the elementary unit of the polymer containing one ionogenic group. For example, for a sulfonated resin based on styrene and divinylbenzene, the elementary unit corresponds to the formula C8H85O3, therefore, its theoretical weight capacity will be 1000 / 184 2 5 43 mEq per 1 g of dry resin in the H - form.
If the filtration continues until the moment of complete equalization of the concentrations of the absorbed ion in the source water and the filtrate, then almost the entire absorption capacity of the ion exchanger for this ion is used. This mode corresponds to the use of the full exchange capacity of the OEP ion exchanger.
If we continue passing the solution through the ion exchanger layer, then there will come a moment when the concentrations of the solutions - the initial and the ones flowing from the filter - become equal. This makes it possible to calculate the total exchange capacity of the ionite.
If we continue passing the solution through the ion exchanger layer, then there will come a moment when the concentrations of the solutions - the initial and the ones flowing from the filter - will be equal. This makes it possible to calculate the total exchange capacity of the ionite.
A promising direction is the use of a mixed layer of cation exchangers and anion exchangers on pre-wash filters - the so-called paudex process. Such filters have a much greater use of the total exchange capacity of the ion exchangers.
The total (total) exchange capacity of the cation exchanger is determined by neutralization with a solution of NaOH or KOH under static or dynamic conditions and is expressed in equivalents per 1 g of dry or 1 dm 3 of swollen cation exchanger.
Cation exchange reactions (K-cation exchanger) have the form:
Substances that do not dissociate in solutions are adsorbed by ion exchangers, as on active carbon, according to the laws of molecular adsorption.
The total exchange capacity of various grades of strongly acidic cation exchangers used in the sugar industry ranges from 4 to 6 meq/g. For example, the domestic cation exchanger KU-2-8/N, Na ionic form/ has a total exchange capacity of 5.1 /N/mg-eq/g.
Purpose of analysis - evaluate the quality and suitability of the cation exchange resin for the purification of sugar solutions.
Principle of analysis method is based on the titration of the acid formed as a result of the ion exchange reaction with 0.1 N. NaOH solution in the presence of methyl orange as an indicator.
Reagents:
5% NaCl solution;
0.1 N NaOH solution;
The indicator is methyl orange.
Devices and materials:
Glass column with a diameter of 18 mm, a height of 250 cm with a drawn end;
drip funnel;
Volumetric flask with a capacity of 200 cm 3;
Measuring cylinder with a capacity of 100 cm 3;
Burette for titration;
Beaker;
cation exchange resin.
Definition progress
5 g of the H-form cation exchanger prepared for analysis is transferred to a glass column with a diameter of 18 mm using distilled water; To prevent entrainment of the cation exchanger, a glass wool swab is placed on the glass lattice of the column.
After that, 100 cm 3 of a 5% solution of chemically pure NaCl is uniformly passed from a dropping funnel installed above a column with a cation for 30 min, maintaining the level of the solution above the cation exchanger layer equal to 1 cm. Then the cation exchanger is washed with double its volume of water. The filtrate and washings are collected in a volumetric flask, where their volume is brought to 200 cm 3 . From this volume, 50 cm 3 are taken into a separate beaker and titrated with 0.1N. NaOH solution in the presence of methyl orange as an indicator.
Calculations:
1. To obtain comparable results, the exchange capacity of the cation exchanger is expressed in milligram equivalent of ions / or the number of active groups / per 1 g of dry ion exchanger. Therefore, if the flow rate is 0.1N. NaOH solution to neutralize the acid isolated by 1 g of absolutely dry cation exchanger can be expressed by the formula
,
and in 1 cm 3 1 n. NaOH solution contains 0.1 mg-eq, then the total exchange capacity of the cation exchanger can be calculated from the formula
Where Ek- full exchange capacity, in mg-eq/g of absolutely dry cation exchanger;
b- total amount of filtrate, cm 3 ;
V- the amount of 0.1 n. NaOH solution used for titration of the filtrate, cm 3;
a is the amount of filtrate taken for titration, cm3;
g - the amount of dry cation exchanger taken to determine its total exchange capacity, g;
W is the moisture content of the cationite, %. Determined by drying for 3 hours at a temperature of 95-100ºС.
2. The exchange capacity of the cation exchanger can also be expressed in terms of sodium. In this case, the calculation is carried out according to the formula
or, since 1 cm 3 0.1 n. NaOH solution contains 0.0023 g of sodium, then 
.
Introduction
The total exchange capacity of the anion exchange resin is determined by its neutralization with a solution of HCl or H 2 SO 4 under static or dynamic conditions and is expressed in equivalents per 1 g of dry or swollen anion exchange resin.
Anion exchange reactions / A-anion exchange resin / have the form:
A. /OH/ +H /Cl = A.OH.Cl +HO;
A. /OH/ + H /SO = A.SO +2HO.
In addition to the exchange capacity, the main indicators of the suitability of the anion exchanger include: discoloration, swelling degree, aging ability, insolubility in water and organic solvents, ease of regeneration, thermal and mechanical strength.
The total exchange capacity of various grades of anion exchangers used in the sugar industry can be 1–10 meq/g. The domestic macroporous anion exchange resin AV-17-2P used for bleaching sugar solutions has a total exchange capacity of 0.1 N. HCl solution 3.8 mg-eq / g, and 0.1 n. NaCl solution 3.4 mg-eq/g.
Purpose of analysis - evaluate the quality of the anion exchange resin for decolorizing sugar solutions.
Principle of analysis method is based on the titration of a 0.1 N acid solution not absorbed by the anion exchanger. NaOH solution.
Reagents:
0.1 N HCl and NaOH solutions.
Devices and materials:
A glass column with a diameter of 18 mm, a height of 250 mm, with an end drawn in the lower part, on which a rubber tube with a screw clamp is put on;
glass funnel;
Volumetric flask for 500 cm 3;
Burette for titration;
Beaker;
anion exchange resin.
Definition progress
10 g of the anion exchanger prepared for analysis in OH - form is transferred with water into a glass column with a diameter of 18 mm with a glass wool swab at the bottom, and excess water is drained through a rubber tube with a screw clamp.
After that, 400 cm 3 of 0.1 n. HCl solution, maintaining the level of the solution above the anion exchanger layer equal to 1 cm. Then it is washed with double the volume of the anion exchanger with water. The filtrate and washings are collected in a volumetric flask and brought to a volume of 500 cm 3 . Selected from the total volume in a glass of 50 cm 3 and titrated with 0.1 N. NaOH solution.
Calculations:
1. To obtain comparable results, the exchange capacity of the anion exchanger is expressed in the same way as the cation exchanger in terms of mg-eq / g of dry ion exchanger.
Therefore, if 1 g of absolutely dry anion exchanger absorbs
cm 3 0.1 n. HCl solution, and 1 cm 3 of this solution contains 0.1 mg-eq / g, then the total exchange capacity of the anion exchange resin E A can be calculated from the formula
,
Where E A- total exchange capacity of the anion exchanger, mg-eq/g of absolutely dry ion exchanger;
a- amount of filtrate collected for titration, cm 3 ;
V O - the amount of 0.1 n. HCl solution passed through the anion exchanger, cm 3;
Vb- total amount of filtrate, cm 3 ;
g- the amount of dry anion exchange resin taken to determine its capacity, g;
W is the moisture content of the anionite, %. Determined by drying for 3 hours at 95-100˚C.
2. The capacity of the anion exchanger can also be expressed as a percentage of HCl. In this case, take into account the fact that 1 cm 3 0.1 n. HCl solution contains 0.0036 g HCl, calculation of E is carried out according to the formula
6.3. Regeneration of ion exchange resins
Introduction
The ion-exchange resins spent in the working cycle are subjected to regeneration (recovery) after they are washed with water.
Cation exchangers are reduced with weak solutions of HCl and HSO
K.Na + H /SO = K.H + Na /SO;
KNa + HCl = KH + NaCl.
For the reduction of anion exchangers, weak solutions of NaOH, KOH, NaCl, etc. are used.
A.OH.Cl + Na /OH = A./OH/ + Na /Cl.
At the end of the regeneration cycle, the acidity of the regenerate from the cation exchanger or the alkalinity of the regenerate from the anion exchanger should approach the acidity and alkalinity of the regeneration solutions. The end of regeneration is determined by titration.
Purpose of analysis - restore the exchange capacity of ion exchangers.
Principle of analysis method based on the titration of regeneration solutions from a cation exchanger 0.1 N. NaOH solution, and from the anion exchanger - 0.1 n. HCl solution.
Reagents:
5% HCl solution;
4% NaOH solution;
0.1 N NaOH solution;
0.1 N HCl solution.
Devices and materials:
Glass columns with cation exchange resin and anion exchange resin.
Definition progress
After washing the resin with water, regeneration is carried out in the columns: cation exchanger - with 5% HCl solution, and anion exchanger - with 4% NaOH solution, passing them at a rate of 20 cm 3 /min.
The end of the regeneration of the cation exchanger is established by titration of its regeneration solutions with 0.1 N. NaOH solution, and an anion exchanger - 0.1 n. HCl solution.
After regeneration, the cation exchanger is washed with water until a neutral or slightly acidic reaction, and the anion exchanger - until a neutral or slightly alkaline reaction.
Control questions
1. What is ion exchange?
2. What are ion exchange resins?
3. What ion exchange resins are used in sugar production?
4. Tell us about the static and dynamic exchange capacity of ion exchangers?
5. What determines the total exchange capacity of ion exchangers?
6. In what units is the total exchange capacity expressed?
7. What is the purpose of using ion exchangers in sugar production?
8. On what principle is the determination of the total exchange capacity of ion exchangers based?
9. Why is ion exchange resin regenerated?
10. On what principle is the regeneration of ion exchangers based?
11. How is the end of the ion exchanger regeneration process determined?
Lab #7
Analysis Wastewater sugar production
Introduction
IN Food Industry the largest number water is consumed by sugar refineries. If for the needs of the sugar beet plant only clean water from natural reservoirs, without returning part of the waste water to production, then total consumption industrial (fresh) water will be 1200-1500% by weight of beets. It is possible to reduce the consumption of fresh water to 150-250% by weight of the beet, provided that waste water is used in many areas of the sugar plant according to the circulating water supply scheme. Artesian water is used only for washing granulated sugar in centrifuges, for pumping the massecuite Ι crystallization and for the needs of the factory laboratory.
Waste (waste) waters of sugar factories are diverse in their physical and chemical composition, the degree of pollution and the method of required purification. According to the degree of pollution, they are classified into three categories. Each category is divided into two subgroups: A and B, of which the water of subgroup A is better in quality than subgroup B.
Wastewater from sugar production contains a large amount of organic matter, and their treatment in natural conditions is associated with certain difficulties, requires significant land areas and can have a negative impact on environment. IN last years a number of biological treatment methods and appropriate equipment for their implementation have been developed. The currently proposed purification methods are mainly based on anaerobic and aerobic processes for the decomposition of sewage impurities from sugar and starch factories.
Modern technology wastewater treatment consists in the sequential separation of the impurities contained in them by mechanical, anaerobic and aerobic methods. At the same time, the anaerobic method is a new process in wastewater treatment technology. The anaerobic purification process requires maintaining temperatures in the range of 36-38 0 С for its implementation, which is associated with additional heat consumption. Its difference from the widespread aerobic method lies primarily in the minimal growth of biosludge and the conversion of carbohydrate-containing impurities into biogas, the main component of which is methane.
Aerobic process
C 6 H 12 O 6 + O 2 ---- CO 2 + H 2 O + Bioprecipitate + Heat (6360 kJ).
anaerobic process
C 6 H 12 O 6 ---- CH 4 + CO 2 + Bioprecipitate + Heat (0.38 kJ).
Anaerobic methods are divided into four main groups according to the type of reactors used in the purification processes:
With recirculation of biosludge (activated sludge):
With a layer of anaerobic sediment and its internal sedimentation;
With inert fillers for biosludge;
Special.
Wastewater subjected to anaerobic treatment should contain as little as possible mechanical impurities and substances that inhibit the methanogenic process. A hydrolysis-acid phase must pass in them, and in addition, wastewater must have a certain pH value and a temperature in the range of 36-38 0 С.
It is believed that the anaerobic treatment method is economically beneficial for wastewater with pollution of more than 1.2-2.0 g/dm 3 BOD 5 (biological oxygen demand). The upper limit of pollution is not limited. It can be equal to 100 g / dm 3 COD (chemical oxygen demand).
These include:
A) Excess fresh water from the pressure tank, from the cooling of the massecuite in massecuite mixers, from pumps and other installations with a temperature below 30 ° C. These waters do not require treatment to be returned to production;
B) Barometric, ammonia and others with temperatures above 30°C. To return these waters, pre-cooling and aeration is required.
To wastewater category II include conveyor-washing water from hydraulic conveyors and beet washers. For the reuse of these waters in production, their preliminary mechanical purification is required by settling in special settling tanks.
To wastewater category III include: pulp press water, its sludge, laver water, conveyor-washing water sediment, liquid filtration sediment, household, fecal and other harmful waters. Category III water treatment requires biological and combined treatment methods in appropriate sedimentation tanks and filtration fields.
At existing sugar factories, the following main indicators of water balance (% by weight of beets) are taken as a basis: fresh water intake from a reservoir - 164; the number of recycled waters of category I - 898; II category -862; wastewater of category III - 170 or 110, provided that the suspension of the conveyor-washing sludge is settled in vertical settling tanks-thickeners Sh1-POS-3 and the decantate is returned to the recirculation circuit of waters of category II.
For newly built sugar beet factories, the consumption of fresh water for production needs should not exceed 80% by weight of beets, and the amount of treated industrial wastewater discharged into natural water bodies should not exceed 75% by weight of beets.
When analyzing the quality of industrial and waste water, their temperature, color, odor, transparency, sludge characteristics, suspended solids content, dry residue, pH, total alkalinity (acidity), oxidizability, biochemical oxygen demand (BOD), chemical oxygen demand (COD), concentration of ammonia, nitrates, chlorides and other indicators are determined.
Goal of the work - master the methods of quality control of industrial (fresh) and waste water.
