Method for evaluating the effectiveness of a dechlorination process of a liquid and method for improving the efficiency of such process and measuring device for these processes

Abstract

The invention relates to a device for measuring the concentration of at least one gaseous component of a dechlorination process of a liquid, to a method for evaluating the effectiveness of a dechlorination process of a liquid and a method for improving the efficiency of a repetitive or continuous dechlorination process of a liquid. The invention further relates to a use of the measuring device for measuring the concentration of at least one gaseous compound obtained from a process stream.

Description

[0001] VESTOLIT GmbH 14.08.2024

[0002] P62594WO /

[0003] - 1 -

[0004] Method for Evaluating the Effectiveness of a Dechlorination Process and Method for Improving the Efficiency of such Process and Measuring Device for these Processes

[0005] Technical field

[0006] The invention relates to a measuring device usable in a method for evaluating the effectiveness of a dechlorination process and in a method for improving the efficiency of such dechlorination process.

[0007] Background of the invention

[0008] In general, liquid and gaseous process streams can contain undesired chlorine compounds. Their removal can pose serious difficulties. For example when chlorine, alkaline metal hydroxide and hydrogen are produced by electrolysis of a brine, such as an alkali metal chloride solution, a depleted brine (membrane technology) or brine / caustic-liquor (diaphragm technology) is obtained. The chlorine in the liquid can negatively impact the following equipment such as filters, ionexchangers, evaporators and more, which can lead to a heavy corrosion and / or a reduced efficiency of the electrolysis. As further example, a process stream such as a waste water solution can comprise undesired chlorine compounds if, for instance, the waste water stream is obtained from a gas scrubber, which is used for treatment of waste gas obtained from combustion of residual and / or waste materials. These chlorine compounds need to be removed prior disposal of the process stream since chlorine compounds are known to cause environmental harm even at low concentrations and are especially harmful for organisms living in soil and water.

[0009] Reducing the amount of chlorine compounds in process streams requires dechlorination of the process stream. Various methods of physical dechlorination as well as chemical dechlorination are known. As an example for physical dechlorination, a vacuum can be used to remove chlorine gas from the process stream. As a further example for physical dechlorination, hypochlorite compounds VESTOLIT GmbH 14.08.2024

[0010] P62594WO /

[0011] - 2 - present in the process stream can be decomposed to sodium chloride and oxygen by using electromagnetic radiation. As an example for chemical dechlorination, a reducing agent such as sodium bisulfite can be added to the process stream to reduce chlorine compounds under the formation of sodium chloride and sodium sulfate. To be on the safe side, agents used for chemical dechlorination, such as reducing agents, are often overdosed to ensure sufficient removal of chlorine compounds.

[0012] For evaluating the efficiency of the physical and chemical dechlorination and for optimizing the dechlorination, the amounts of chlorine and hypochlorite compounds remaining in the process stream following dechlorination need to be determined. Prior art methods, as described in WO 2007 / 130851 , determine the amount of hypochlorite by using an oxidation-reduction potential (ORP) sensor. However, amperometric methods for measuring hypochlorite are sensitive to changing process parameters such as pressure, pH value or chloride content. As a consequence, the measured concentration of chlorine and hypochlorite compounds are often reported too high by such methods.

[0013] In Birkmann et al. (Development of a Measuring Method for the Determination of Bisulfite and Sulfite in Seawater), published September 11 , 2019, a UV spectroscopy with multivariate analysis methods is described for optimizing the use of bisulfite and reducing agents. The combination of UV spectroscopy and chemometric evaluation methods are seen to be suitable for aqueous applications and for the monitoring of waste water. However, pretreatment of the water is recommended to improve the analytical quality when aiming to optimize the feed of reducing agents.

[0014] The prior art methods known to us have the disadvantage that the chlorine and hypochlorite compounds remaining in the process stream cannot be accurately determined and, consequentially, the amount of chlorine in a liquid or gaseous process stream cannot be reduced reliably. As a consequence, the dechlorination of VESTOLIT GmbH 14.08.2024

[0015] P62594WO /

[0016] - 3 - a process stream cannot be optimized due to the difficulties encountered when attempting to measure the remaining chlorine and hypochlorite compounds.

[0017] Thus, it is an object of the present invention to provide a method for improving the efficiency of a dechlorination process of a liquid.

[0018] Summary of the invention

[0019] In a first aspect, the invention is directed to a method for evaluating the effectiveness of a dechlorination process of a liquid according to claim 1 .

[0020] In a second aspect, the invention is directed to a method for improving the efficiency of a repetitive or continuous dechlorination process of a liquid according to claim 11 . This method extends the method of the first aspect by including further method steps.

[0021] In a third aspect, the invention is directed to a device for measuring the concentration of at least one gaseous component of a dechlorination process of a liquid, said device is specified in claim 13.

[0022] In a fourth aspects, the invention is directed to the use of the device according to the third aspect of the invention for measuring the concentration of chlorine and / or the concentration of sulfur dioxide in a method for dechlorinating a liquid.

[0023] In a fifth aspects, the invention is directed to the use of said device for measuring the concentration of chlorine and / or the concentration of sulfur dioxide in a method for evaluating the effectiveness of a dechlorination process of a liquid.

[0024] Figures

[0025] Figure 1 : schematic presentation of an exemplary embodiment of the measuring device of the invention. VESTOLIT GmbH 14.08.2024

[0026] P62594WO /

[0027] - 4 -

[0028] Detailed description of the invention

[0029] It has been found that the difficulties of measuring chlorine and hypochlorite compounds, which remain in a liquid process stream following dechlorination, can be overcome when measuring the concentration of gaseous compounds such as chlorine gas in a gas stream. It is therewith no longer necessary to conduct a pretreatment of the process stream in order to improve the analytic quality by adjusting process parameters, such as pressure, pH value or chloride content.

[0030] When a process stream comprises chlorine gas and water, both components form an equilibrium with hypochlorite compounds and hypochloric acid: equation 1

[0031] The equilibrium is dependent on the reaction conditions, such as the temperature, the pressure, and the concentration of the individual components.

[0032] In the presence of sodium hydroxide, the hypochlorite compounds further react to sodium hypochlorite:

[0033] H+’OCI + H+CI-+ 2 Na+OH — > Na+OCI’ + Na+Cl’ + 2 H2O equation 2

[0034] In this case hypochlorite compounds are removed from the equilibrium of equation 1 and the equilibrium is shifted to the right, leading to the consumption of chlorine gas. In the presence of an acid, the equilibrium of equation 1 is however shifted to the left, leading to the liberation of chlorine gas.

[0035] The method of the invention takes advantage of this equilibrium for optimizing the dechlorination of the process stream. To this end, a process stream can be subjected to physical dechlorination and / or chemical dechlorination and a sample of the thus treated process stream can be taken. The sample is acidified by adding, for example, phosphoric acid in excess to the sample. Therewith the equilibrium of equation 1 is shifted to the left and, if chlorine and hypochlorite compounds remain in the process stream following the dechlorination, chlorine gas is liberated: VESTOLIT GmbH 14.08.2024

[0036] P62594WO /

[0037] - 5 -

[0038] Na+OCI’ + Na+Cl’ + H3PO4 (in excess) equation 3 CI2T + H2O + Na2HPO4+ x H3PO4

[0039] Following the degassing of the acidified sample by using a stripping gas, the concentration of at least one gaseous compound can be measured in the obtained gas stream. If undesired gaseous compounds are measured in the gas stream, the physical dechlorination and / or chemical dechlorination may need to be optimized. For example, the effectiveness of the dechlorination step can be determined, if a sample of the process is taken and an acid is added to the sample to liberate and measure the concentration of chlorine gas. If chlorine gas is detected, physical and / or chemical dechlorination may be optimized by adjusting the dechlorination parameters to further reduce the amount of chlorine and hypochlorite compounds present in the process stream following dechlorination.

[0040] Thus, the above mentioned object of the invention is solved, in an initial aspect of the invention, by a method for evaluating the effectiveness of a dechlorination process of a liquid, the method comprising the steps of:

[0041] (i) providing a liquid, the liquid comprising water, an initial amount of chlorine CI2 in equilibrium with a hypochlorite compound CIO-;

[0042] (ii) optionally, adding an amount of a sulfite reducing agent to the liquid thereby chemically reducing the CIO- compound to a chloride compound Cl-;

[0043] (iii) taking a sample of the liquid after step (i) or, if present, after step (ii);

[0044] (iv) adding an excess amount of an acid to the sample, which shifts the equilibrium between the CI2 and the CIO- compound to the CI2;

[0045] (v) eventual forming of sulfur dioxide SO2 by a reaction of the added acid with the added sulfite reducing agent, wherein the forming depends on the initial amount of the CI2 and the amount of the added acid and, if added, the amount of the sulfite reducing agent;

[0046] (vi) obtaining a modified sample of the liquid comprising amounts of either CI2 or SO2 or comprising substantially no amounts of CI2 and SO2; VESTOLIT GmbH 14.08.2024

[0047] P62594WO /

[0048] - 6 -

[0049] (vii) degassing the modified sample of the liquid using a stripping gas, thereby obtaining a gas stream comprising either CI2 or SO2 or being substantially free of CI2 and SO2;

[0050] (viii) a) measuring the concentration of CI2 in the gas stream by using a CI2 gas detector, and, if no CI2 or a quantity of CI2 that falls below a predetermined threshold is detected but the sulfite reducing agent was added, measuring the concentration of SO2 in the gas stream by using a SO2 gas detector, or b) if the sulfite reducing agent was added, measuring the concentration of SO2 in the gas stream by using a SO2 gas detector, and, if no SO2 or a quantity of SO2 that falls below a predetermined threshold is detected, measuring the concentration of CI2 in the gas stream by using a CI2 gas detector;

[0051] (ix) classifying the result(s) of the measurement(s) as follows: a) if the measured CI2 concentration exceeds a predetermined threshold the added amount of the sulfite reducing agent was too low, or b) if the measured SO2 concentration exceeds a predetermined threshold the added amount of the sulfite reducing agent was too high, or c) if the measured CI2 concentration or the measured SO2 concentration does not exceed a predetermined threshold the added amount of the sulfite reducing agent was adequate.

[0052] By using this method, it is possible to rapidly measure at least one gaseous compound present in the gas stream as the measured result can be obtained in under 2 minutes due to the quick sample preparation without the need to adjust process parameters. The method thus provides a quick and reliable way to determine the presence of chlorine and hypochlorite compounds and to optimize the dechlorination of a process stream. It is a further advantage of the method that the process stream can be analysed continuously. The dechlorination efficiency can therefore be permanently evaluated and optimized without any major delay.

[0053] In step (i) the liquid may comprise the chlorine and hypochlorite compounds in an amount of up to 100 g per kg of the liquid. However, the concentration of the VESTOLIT GmbH 14.08.2024

[0054] P62594WO /

[0055] - 7 - chlorine and hypochlorite compounds may also be higher or lower depending on the liquid or the process performance the liquid is taken from.

[0056] Optionally, the inventive method may further comprise a step of subjecting the liquid to a physical pre-dechlorination and / or a chemical pre-dechlorination, thereby obtaining a liquid comprising a reduced amount of CI2. This further step may take place between step (i) and (ii) or, if step (ii) is not present, between step (i) and step (iii). In case a physical pre-dechlorination is performed this can be done, for example, by removing chlorine gas from the liquid by vacuum dechlorination or by decomposing hypochlorite compounds to sodium chloride and oxygen by using electromagnetic radiation with a wavelength from about 10 to 400 nm. In case a chemical pre-dechlorination is performed this can be done, for example, by removing hypochlorite compounds by adding hydrogen peroxide and alkali metal hydroxide to the liquid or is performed by a catalytic decomposition of hypochlorite compounds.

[0057] If in step (ii) the liquid is subjected to chemical dechlorination by adding a sulfite reducing agent, the reducing agent can be added as aqueous solution, preferably the reducing agent can be added in small molar excess compared to the hypochlorite concentration of the liquid. The reducing agent can preferably comprise sodium bisulfite. Sodium bisulfite may be added as aqueous solution having a concentration of 2 to 60 wt.-% sodium bisulfite based on the aqueous solution, preferably 5 to 55 wt.-% sodium bisulfite based on the aqueous solution, more preferably 15 to 45 wt.-% sodium bisulfite based on the aqueous solution, or most preferably 25 to 35 wt.-% sodium bisulfite based on the aqueous solution.

[0058] Regarding the optional step of physical pre-dechlorination, this step can include removing chlorine gas from the liquid by vacuum dechlorination and / or the physical pre-dechlorination can include decomposing hypochlorite compounds to sodium chloride and oxygen by using electromagnetic radiation with a wavelength from about 10 to 400 nm. Preferably, hypochlorite compounds are decomposed to alkali metal or hydrogen chloride and oxygen by using a wavelength of 100 to 300 nm. Exemplary conditions for conducting vacuum dechlorination are vacuum pressure below 0.1 MPa (1 bar) and elevated temperatures like 80 °C. Exemplary conditions VESTOLIT GmbH 14.08.2024

[0059] P62594WO /

[0060] - 8 - for decomposing hypochlorite compounds by electromagnetic radiation are limited by the properties of the required glass equipment at ca. 50 °C and a pH below 11 .

[0061] Regarding the optional step of chemical pre-dechlorination, this step can include removing hypochlorite compounds by adding hydrogen peroxide and alkali metal hydroxide, such as potassium hydroxide and / or sodium hydroxide, to the liquid. In addition or as alternative, the chemical pre-dechlorination can include catalytic decomposition of hypochlorite compounds, for example, as described in JP 2014065002 A and CN 105800706 A. As example, the hypochlorite compounds in the liquid can be decomposed by the use of active carbon. In this reaction active carbon reacts with the hypochlorite species (NaOCI or HOCI) to CO2and the corresponding chloride component (NaCI or HCI). Exemplary conditions for decomposing hypochlorite compounds using active carbon are a temperature of around 20 °C (room temperature), a pH of the liquid containing hypochlorite compounds of around 10 and a flow rate of the liquid stream of about 6 m / h. Under this condition, around 400-800 ppm (w / w) of sodium hypochlorite can be decomposed at a decomposing rate of around 0.5 g hypochlorite compounds per g active carbon (as described in Kenzo ABE, Masanori KIMURA, Hiroo YAMADA, Decomposition of sodium hypochlorite solution with activated carbon, Journal of Japan Society of Air Pollution, 1981 , Volume 16, Issue 6, Pages 422-425). The hypochlorite compounds can therewith be decomposed to oxygen and chloride ions. In a further example, chemical pre-dechlorination may include catalytic decomposition of hypochlorite to alkali metal chloride and oxygen by using a nickel catalyst. A suitable nickel catalyst is HYDECAT™ obtainable by Johnson Matthey Chemicals GmbH. Exemplary conditions for a catalytic decomposition by using a nickel catalyst are at low temperatures from 10 to 50 °C (50-120 °F) and at a pH range from 9 to 14.

[0062] The above described physical and chemical pre-dechlorination methods may be combined, thus the liquid may be subjected to one or more physical and / or one or more chemical pre-dechlorination steps. Preferably, the liquid is subjected to physical pre-dechlorination, such as vacuum dechlorination, and chemical pre- dechlorination, such as adding a reducing agent to the process stream.

[0063] When in step (ii) the reducing agent is added to the liquid the hypochlorite compound present in the process stream reacts with the reducing agent:

[0064] Na+OCI- + NaHSO3+ Na+OH’ Na2SO4+ Na+Cl’ + H2O equation 4 VESTOLIT GmbH 14.08.2024

[0065] P62594WO /

[0066] - 9 -

[0067] Preferably, when adding bisulfite as the reducing agent to the process stream, a Bronsted base such as sodium hydroxide is additionally added to the process stream to adjust the pH of the process stream.

[0068] If the reducing agent is overdosed, the remaining reducing agent such as sodium bisulfite present in the process stream and hence present in the sample of step (iii) reacts with the acid added in step (iv):

[0069] NaHSOs + H3PO4— > SChf + H2O + NaH2PO4 equation 5

[0070] As a consequence, if the reducing agent is overdosed, sulfur dioxide is liberated. To optimize the dechlorination when using the reducing agent, it is thus beneficial to measure the concentration of sulfur dioxide in the gas stream.

[0071] Typically, the hypochlorite compound CIO- is hypochlorous acid and / or a salt thereof.

[0072] In the method according to the invention, the sulfite reducing agent can be selected, for example, from sodium bisulfite NaHSOs, sodium metabisulfite Na2S20s, sodium sulfite Na2SO3, and combinations thereof. Preferably, the sulfite reducing agent is sodium bisulfite NaHSOs.

[0073] The liquid that is the subject of the dechlorination process can be a liquid process stream, for example, an aqueous process stream. As a specific example a brine comprising water, chlorine, alkali metal chloride, alkali metal hydroxide, and hypochlorite compounds is mentioned. The brine can be obtained, for example, after an electrolytic conversation of a concentrated brine comprising water and alkali metal chloride. The liquid can be a brine containing alkali metal chloride in an amount of up to 360 g per kg of the liquid, preferably 50 to 300 g per kg of the liquid, more preferably 100 to 250 g per kg of the liquid, most preferably 150 to 200 g per kg of the liquid when measured at 20 °C.

[0074] In an alternative embodiment of the invention, the liquid can be a washing solution comprising chlorine and hypochlorite compounds. For example, the washing VESTOLIT GmbH 14.08.2024

[0075] P62594WO /

[0076] - 10 - solution can be obtained from a gas scrubber. The gas scrubber may be used, for example, for treatment of waste gas obtained from combustion of residual and / or waste materials comprising chlorine and hypochlorite compounds.

[0077] The steps (iv) to (viii) can be conducted at a temperature in the range of -21 °C to 108 °C. Preferably, these steps are conducted at a temperature in the range of 0 °C to 100 °C, and more preferably at a temperature in the range of 10 °C to 90 °C.

[0078] If the liquid is a brine, steps (iv) to (vi) can be conducted at a temperature in the range of -21 to 108 °C, preferably in the range of 10 to 100 °C, more preferably in the range of 40 to 100 °C and most preferably in the range of 60 to 90 °C.

[0079] If the liquid is a waste water stream comprising chlorine and hypochlorite compounds, such as a waste water stream obtained from a gas scrubber, steps (iv) to (vi) can be conducted at a temperature in the range of -21 to 108 °C, preferably in the range of 10 to 100 °C, more preferably in the range of 10 to 70 °C and most preferably in the range of 10 to 50 °C.

[0080] A suitable pressure for conducting steps (iv) to (vi) is atmospheric pressure, i.e. 101.3 kPa. The pressure of the sample in step (iii) is depending on the process parameters. To release any excess pressure, a portion of the sample may be discharged before step (iv).

[0081] A suitable pH of the process stream treated with bisulfite is above pH 6. However, since the sample taken from the process stream is acidified to liberate the gaseous compounds and degassed to obtain a gas stream, adjusting the pH of the process stream is not necessary for conducting the method for optimizing the dechlorination of a process stream.

[0082] In step (iii), the sample can be taken continuously or in intervals. It is preferred that the sample is taken continuously. If the sample is taken continuously, the volume of the sample acidified in step (iv) may be 0.1 to 1000 ml / min. Most preferably the volume of the sample is in a range of 0.5 to 5 ml / min. VESTOLIT GmbH 14.08.2024

[0083] P62594WO /

[0084] - 11 -

[0085] Following step (iii) the sample may be at least in part reused. For instance, the sample can be at least in part reused in industrial processes, e.g. for electrolytic conversion of a brine to a depleted brine comprising chlorine gas and sodium hydroxide. In the alternative, following step (iii) the sample is not reused.

[0086] In the method according to the invention, the acid can be selected from the group consisting of hydrochloric acid, phosphoric acid, nitric acid and combinations thereof. Preferably, the acid is phosphoric acid. Further preferably, the acid is 5 to 30 vol.-% phosphoric acid, most preferably the acid is 10 to 20 vol.-% phosphoric acid.

[0087] In step (iv), the acid can be added in a volume ratio of acid to sample in the range of 10:1 to 1 :10, preferably in a volume ratio of acid to sample in the range of 1 :1 to 1 :10, more preferably in a volume ratio of acid to sample in the range of 1 :2 to 1 :6, most preferably in a volume ratio of acid to sample of 1 :4.

[0088] In step (iv) a defined small volume of the sample is acidified. The volume of the sample may be in a range of 0.1 to 50 ml. Most preferably the volume of the sample is in a range of 1 to 5 ml.

[0089] When degassing the acidified sample using a stripping gas in step (v), the stripping gas may be an inert gas, nitrogen and / or ambient air.

[0090] Regarding step (viii), i.e. the measuring of the concentration of the gaseous compounds present in the gas stream, suitable gas detectors for detecting chlorine gas or sulfur dioxide can be, for instance, obtained from Drager (article no.: 6809665 and 6809660).

[0091] According to the invention, the result or the results of the measurement or the measurements of step (viii) is / are preferably transmitted to a process control system. The process control system can be configuered to automatically classify the transmitted result(s) of the measurement(s) as provided in step (ix).

[0092] The method of the present invention, i.e. for evaluating the effectiveness of a dechlorination process, can be extended to a method for improving the efficiency of VESTOLIT GmbH 14.08.2024

[0093] P62594WO /

[0094] - 12 - a repetitive or continuous dechlorination process of a liquid. In this case the method as described above is further specified as follows:

[0095] (i) the liquid is provided in form of a liquid process stream; and the following steps are added:

[0096] (x) adjusting the amount of the sulfite reducing agent added to the liquid by taking one of the following actions: a) if the added amount of the sulfite reducing agent was too low, repeat steps (ii) to (ix) of the dechlorination process but with an increased amount of the sulfite reducing agent added in step (ii), b) if the added amount of the sulfite reducing agent was too high, repeat steps (ii) to (ix) of the dechlorination process but with an decreased amount of the sulfite reducing agent added in step (ii), or c) if the added amount of the sulfite reducing agent is adequate, repeat steps (ii) to (ix) of the dechlorination process with constant amount of the sulfite reducing agent added in step (ii); and

[0097] (xi) repeating steps (ii) to (xi) while operating the dechlorination process.

[0098] According to this further aspect of the invention, the process control system may automatically classify the transmitted result(s) of the measurement(s) as provided in step (ix), and, based on the classification, may automatically adjusts the amount of the sulfite reducing agent added to the liquid in step (ii) as provided in step (x).

[0099] The third aspect of the invention is directed to a device for measuring the concentration of at least one gaseous component of a dechlorination process of a liquid. This measuring device comprises:

[0100] (i) a sample transport line configured and arranged to receive and feed through a sample of a liquid, the liquid comprises water, and eventually either chlorine CI2 in equilibrium with a hypochlorite compound CIO- or sulfur dioxide SO2, or eventually comprises water being substantially free of CI2 and SO2;

[0101] (ii) a first supply line configured and arranged to feed an acid into the sample transport line so that an acidified sample is formed; VESTOLIT GmbH 14.08.2024

[0102] P62594WO /

[0103] - 13 -

[0104] (iii) downstream from the first supply line a second supply line configured and arranged to feed a stripping gas into the sample transport line so that a sample mixture comprising the acidified sample and the stripping gas is formed;

[0105] (iv) downstream from the second supply line a gas-liquid separator configured to separate gaseous components from liquid components of the sample mixture, the separator comprises: a) an inlet configured and arranged to let the sample mixture into the separator, b) a first outlet configured and arranged to let the liquid components out of the separator, and c) a second outlet configured and arranged to let the gaseous components out of the separator as a gas stream;

[0106] (v) downstream from the second outlet a gas transport line configured and arranged to feed through the gas stream; and

[0107] (v) a detector unit configured and arranged to receive the gas stream, the detector unit comprises at least one gas detector for measuring the concentration of chlorine CI2 and at least one gas detector for measuring the concentration of sulfur dioxide SO2, the detector unit further comprises an outlet configured and arranged to discharge the gas stream.

[0108] The provided measuring device has the advantage that a sample of a liquid can be analysed continuously or in intervals. The sample is acidified and the gaseous compounds are separated from the liquid compounds. The concentration of gaseous compounds, namely chlorine gas and / or sulfur dioxide, can be measured and the measured concentration can be used to adjust the dechlorination of the liquid. The measuring device thus provides a quick and reliable way of controlling the dechlorination of a liquid. Due to the compactness of the measuring device and the quick sample preparation, the measured result may be obtained in under 2 minutes. The measuring device thus provides a quick and reliable way to determine the presence of chlorine and hypochlorite compounds or the presence of sulfur dioxide resulting from the reduction agents in the liquid. It is a further advantage of the measuring device that the liquid can be analysed continuously. The dechlorination efficiency can therefore be permanently evaluated and optimized without any major delay. VESTOLIT GmbH 14.08.2024

[0109] P62594WO /

[0110] - 14 -

[0111] The measuring device of the invention takes advantage of the equilibrium of chlorine gas and water with hypochlorite compounds and hypochloric acid for optimizing the dechlorination of a liquid. To this end, a sample of a liquid comprising chlorine and hypochlorite compounds is provided. The sample is acidified after entering the measuring device. Therewith, the equilibrium of equation 1 is shifted to the left and, if chlorine and hypochlorite compounds are present in the sample, chlorine gas is liberated as shown in equation 3.

[0112] The measuring device can be used to analyse any liquid, any liquid process stream, or any aqueous process stream each of which comprises chlorine and hypochlorite compounds.

[0113] To separate the vapor phase from the acidified sample (vapor-liquid mixture) a stripping gas is added to the sample. The mixture of the acidified sample and the stripping gas is degassed in a gas-liquid separator and the concentration of at least one gaseous compound is measured in the obtained gas stream. Depending on the gaseous compounds measured in the gas stream, the dechlorination process stream can be optimized. For example, the effectiveness of the dechlorination can be determined, if a sample of the process is taken and an acid is added to the sample to liberate and measure the concentration of chlorine gas. The measured concentration of chlorine gas can subsequently be used to adjust and optimize the dechlorination of the liquid.

[0114] In a preferred embodiment, the measuring device is a measuring device for optimizing the dechlorination of a process stream according to the method of the invention as described above.

[0115] The detector unit can comprise at least one gas detector for measuring the concentration of chlorine gas and at least one gas detector for measuring the concentration of sulfur dioxide. Suitable gas detectors for detecting chlorine gas and / or sulfur dioxide can be, for instance, obtained from Drager (article no.: 6809665 and 6809660). The at least one gas detector for measuring the concentration of chlorine gas and / or the at least one gas detector for measuring the concentration of the gas formed by or from the reducing agent may be configured to detect gas in a concentration of 0.01 to 250 ppm, preferably in a concentration of 0.01 to 100 ppm, more preferably in a concentration of 0.01 to 50 ppm. Preferably, VESTOLIT GmbH 14.08.2024

[0116] P62594WO /

[0117] - 15 - the at least one gas detector for measuring the concentration of chlorine gas and / or the at least one gas detector for measuring the concentration of the gas formed by or from the reducing agent may be configured to detect gas in a concentration of >0 to 250 ppm, preferably in a concentration of >0 to 100 ppm, more preferably in a concentration of >0 to 50 ppm. In an alternative embodiment, the at least one gas detector for measuring the concentration of chlorine gas and / or the at least one gas detector for measuring the concentration of the gas formed by or from the reducing agent may be configured to detect gas in a concentration of >0 to 250 ppm, preferably in a concentration of >0 to 100 ppm, more preferably in a concentration of >0 to 50 ppm.

[0118] The sample transport line is configured and arranged to receive and feed through a sample of a liquid, the liquid comprises water, and eventually either chlorine CI2 in equilibrium with a hypochlorite compound CIO- or sulfur dioxide SO2, or eventually comprises water being substantially free of CI2 and SO2. The sample transport line can preferably be configured to receive a sample of a brine comprising water, chlorine, alkali metal chloride, alkali metal hydroxide, and hypochlorite compounds. The brine may be obtained after electrolytic conversion of a concentrated brine comprising water and alkali metal chloride. In an alternative embodiment, the sample transport line can be configured and arranged to receive a sample of a waste water stream comprising chlorine and hypochlorite compounds, such as a waste water stream obtained from a gas scrubber for treatment of waste gas obtained from combustion of residual and / or waste materials comprising chlorine and hypochlorite compounds.

[0119] In an embodiment of the measuring device, a means is configured and arranged to provide the sample transport line with the sample, preferably the means is a pump. The means can be adapted to continuously provide the sample or the means can be adapted to provide the sample in intervals. Preferably the means is adapted to continuously provide the sample.

[0120] The means may be further configured and arranged to provide the acid. Preferably, the means may be configured and arranged to transport the discharged liquid components of the sample mixture to a waste disposal.

[0121] The pressure of the sample provided to the measuring device is identical with the process pressure. To release any excess pressure, the sample transport line may VESTOLIT GmbH 14.08.2024

[0122] P62594WO /

[0123] - 16 - comprise an outlet configured to discharge a portion of the sample. Following the discharge of a portion of the sample, the pressure can be set to atmospheric pressure. The outlet can be arranged to discharge a portion of the sample before the acid is delivered to the sample.

[0124] Preferably, the sample transport line is configured to transport following the discharge of a portion of the sample, a volume of 0.1 to 1000 ml, preferably 0.2 to 500 ml, 0.3 to 250 ml, 0.4 to 100 ml, 0.5 to 50 ml, 0.6 to 20 ml, 0.7 to 20 ml, 0.8 to 15 ml, 0.9 to 10 ml or 1 to 5 ml. In an alternative embodiment, the sample transport line can be configured to transport, following the discharge of a portion of the sample, a volume of 0.1 to 1000 ml / min, preferably 0.2 to 500 ml / min, 0.3 to 250 ml / min, 0.4 to 100 ml / min, 0.5 to 50 ml / min, 0.6 to 20 ml / min, 0.7 to 20 ml / min, 0.8 to 15 ml / min, 0.9 to 10 ml / min or 1 to 5 ml / min.

[0125] In an embodiment of the measuring device, the at least one gas detector for measuring the concentration of chlorine CI2 and the at least one gas detector for measuring the concentration of sulfur dioxide SO2 are each configured to transmit the measured concentration to a process control system. The process control system can be configured to adjust the physical pre-dechlorination and / or to adjust the chemical pre-dechlorination and / or to adjust the dechlorination according to method steps (ii) to (vi) based on the concentration of the chlorine CI2 and / or based on the concentration of the sulfur dioxide SO2.

[0126] According to a fourth aspect, the invention is directed to the use of a device as specified above for measuring the concentration of chlorine and / or the concentration of sulfur dioxide in a method for dechlorinating a liquid.

[0127] According to a fifth aspect, the invention is directed to the use of a device as specified above for measuring the concentration of chlorine and / or the concentration of sulfur dioxide in a method for evaluating the effectiveness of a dechlorination process of a liquid.

[0128] Example

[0129] Figure 1 shows an exemplary embodiment of the measuring device of the invention. The sample is delivered to the sample transport line with vacuum pressure. Subsequently, a portion of the sample is discharged to adjust the pressure to VESTOLIT GmbH 14.08.2024

[0130] P62594WO /

[0131] - 17 - atmospheric pressure before a defined volume of around 1-3 ml / min of the sample is acidified. A defined volume of an acid is delivered to the sample transport line by a first supply line, whereafter a stripping gas is delivered to the sample transport line by a second supply line. In the sample transport line, the mixture of the acidified sample and the stripping gas is transported to a gas-liquid separator, wherein the liquid components are separated from the gaseous components, such as chlorine gas and gas resulting by or from the reducing agent like sulfur dioxide, and the liquid components are discharged. A gas stream containing the gaseous components is further transported to the detector unit comprising a chlorine gas sensor and a sulfur dioxide sensor for measuring the concentration of chlorine gas and sulfur dioxide.

[0132] The gas stream is thereafter discharged. In this exemplary embodiment, a peristaltic pump is used to continuously transport the sample as well as the acid through the measuring device. The pump may further be used to transport and discharge the liquid components following the separation in the gas-liquid separator.

Claims

1. VESTOLIT GmbH 14.08.2024P62594WO / - 18 -Claims1 . A method for evaluating the effectiveness of a dechlorination process of a liquid, the method comprising the steps of:(i) providing a liquid, the liquid comprising water, an initial amount of chlorine CI2 in equilibrium with a hypochlorite compound CIO-;(ii) optionally, adding an amount of a sulfite reducing agent to the liquid thereby chemically reducing the CIO- compound to a chloride compound Cl-;(iii) taking a sample of the liquid after step (i) or, if present, after step (ii);(iv) adding an excess amount of an acid to the sample, which shifts the equilibrium between the CI2 and the CIO- compound to the CI2;(v) eventual forming of sulfur dioxide SO2 by a reaction of the added acid with the added sulfite reducing agent, wherein the forming depends on the initial amount of the CI2 and the amount of the added acid and, if added, the amount of the sulfite reducing agent;(vi) obtaining a modified sample of the liquid comprising amounts of either CI2 or SO2 or comprising substantially no amounts of CI2 and SO2;(vii) degassing the modified sample of the liquid using a stripping gas, thereby obtaining a gas stream comprising either CI2 or SO2 or being substantially free of CI2 and SO2;(viii) a) measuring the concentration of CI2 in the gas stream by using a CI2 gas detector, and, if no CI2 or a quantity of CI2 that falls below a predetermined threshold is detected but the sulfite reducing agent was added, measuring the concentration of SO2 in the gas stream by using a SO2 gas detector, or b) if the sulfite reducing agent was added, measuring the concentration of SO2 in the gas stream by using a SO2 gas detector, and, if no SO2 or a quantity of SO2 that falls below a predetermined threshold is detected, measuring the concentration of CI2 in the gas stream by using a CI2 gas detector;(ix) classifying the result(s) of the measurement(s) as follows:VESTOLIT GmbH 14.08.2024P62594WO / - 19 - a) if the measured CI2 concentration exceeds a predetermined threshold the added amount of the sulfite reducing agent was too low, or b) if the measured SO2 concentration exceeds a predetermined threshold the added amount of the sulfite reducing agent was too high, or c) if the measured CI2 concentration or the measured SO2 concentration does not exceed a predetermined threshold the added amount of the sulfite reducing agent was adequate.

2. The method of claim 1 , further comprising between step (i) and (ii) or, if step (ii) is not present, between step (i) and step (iii), a step of subjecting the liquid to a physical pre-dechlorination and / or a chemical pre-dechlorination, thereby obtaining a liquid comprising a reduced amount of CI2, preferably wherein the physical pre-dechlorination is performed by removing chlorine gas from the liquid by vacuum dechlorination or is performed by decomposing hypochlorite compounds to sodium chloride and oxygen by using electromagnetic radiation with a wavelength from about 10 to 400 nm, and / or wherein the chemical pre-dechlorination is performed by removing hypochlorite compounds by adding hydrogen peroxide and alkali metal hydroxide to the liquid or is performed by a catalytic decomposition of hypochlorite compounds.

3. The method of any of the preceding claims, wherein the hypochlorite compound CIO- is hypochlorous acid and / or salts thereof.

4. The method of any of the preceding claims, wherein the sulfite reducing agent is selected from sodium bisulfite NaHSOs, sodium metabisulfite Na2S20s, sodium sulfite Na2SO3, and combinations thereof, preferably wherein the sulfite reducing agent is sodium bisulfite NaHSOs.

5. The method of any of the preceding claims, wherein the liquid is a liquid process stream, preferably an aqueous process stream, more preferably a brine comprising water, chlorine, alkali metal chloride, alkali metal hydroxide, andVESTOLIT GmbH 14.08.2024P62594WO / - 20 - hypochlorite compounds, most preferably a brine obtained after electrolytic conversation of a concentrated brine comprising water and alkali metal chloride.

6. The method of any of the preceding claims, wherein the liquid is a washing solution comprising chlorine and hypochlorite compounds, preferably is a washing solution obtained from a gas scrubber, more preferably wherein the gas scrubber is used for treatment of waste gas obtained from combustion of residual and / or waste materials comprising chlorine and hypochlorite compounds.

7. The method of any of the preceding claims, wherein steps (iv) to (viii) are conducted at a temperature in the range of -21 °C to 108 °C, preferably at a temperature in the range of 0 °C to 100 °C, more preferably at a temperature in the range of 10 °C to 90 °C.

8. The method of any of the preceding claims, wherein in step (iii) the sample is taken continuously or in intervals, preferably wherein the sample is taken continuously.

9. The method of any of the preceding claims, wherein the acid is selected from the group consisting of hydrochloric acid, phosphoric acid, nitric acid and combinations thereof, preferably wherein the acid is phosphoric acid, more preferably wherein the acid is 5 to 30 vol.-% phosphoric acid.

10. The method of any of the preceding claims, wherein the result(s) of the measurement(s) of step (viii) is / are transmitted to a process control system, preferably wherein the process control system automatically classifies the transmitted result(s) of the measurement(s) as provided in step (ix).11 . The method of any of the preceding claims, wherein the method is extended to a method for improving the efficiency of a repetitive or continuous dechlorination process of a liquid, the method further comprises:VESTOLIT GmbH 14.08.2024P62594WO / - 21 -(i) the liquid is provided in form of a liquid process stream;(x) adjusting the amount of the sulfite reducing agent added to the liquid by taking one of the following actions: a) if the added amount of the sulfite reducing agent was too low, repeat steps (ii) to (ix) of the dechlorination process but with an increased amount of the sulfite reducing agent added in step (ii), b) if the added amount of the sulfite reducing agent was too high, repeat steps (ii) to (ix) of the dechlorination process but with an decreased amount of the sulfite reducing agent added in step (ii), or c) if the added amount of the sulfite reducing agent is adequate, repeat steps (ii) to (ix) of the dechlorination process with constant amount of the sulfite reducing agent added in step (ii);(xi) repeating steps (ii) to (xi) while operating the dechlorination process.

12. The method according to claim 11 , wherein the process control system automatically classifies the transmitted result(s) of the measurement(s) as provided in step (ix), and, based on the classification, automatically adjusts the amount of the sulfite reducing agent added to the liquid in step (ii) as provided in step (x).

13. A device for measuring the concentration of at least one gaseous component of a dechlorination process of a liquid, the measuring device comprises:(i) a sample transport line configured and arranged to receive and feed through a sample of a liquid, the liquid comprises water, and eventually either chlorine CI2 in equilibrium with a hypochlorite compound CIO- or sulfur dioxide SO2, or eventually comprises water being substantially free of CI2 and SO2;(ii) a first supply line configured and arranged to feed an acid into the sample transport line so that an acidified sample is formed;(iii) downstream from the first supply line a second supply line configured and arranged to feed a stripping gas into the sample transport line so that aVESTOLIT GmbH 14.08.2024P62594WO / - 22 - sample mixture comprising the acidified sample and the stripping gas is formed;(iv) downstream from the second supply line a gas-liquid separator configured to separate gaseous components from liquid components of the sample mixture, the separator comprises: a) an inlet configured and arranged to let the sample mixture into the separator, b) a first outlet configured and arranged to let the liquid components out of the separator, and c) a second outlet configured and arranged to let the gaseous components out of the separator as a gas stream;(v) downstream from the second outlet a gas transport line configured and arranged to feed through the gas stream;(v) a detector unit configured and arranged to receive the gas stream, the detector unit comprises at least one gas detector for measuring the concentration of chlorine CI2 and at least one gas detector for measuring the concentration of sulfur dioxide SO2, the detector unit further comprises an outlet configured and arranged to discharge the gas stream.

14. Use of a device as specified in claim 13 for measuring the concentration of chlorine CI2 and / or the concentration of sulfur dioxide SO2 in a method for dechlorinating a liquid.

15. Use of a device as specified in claim 13 for measuring the concentration of chlorine CI2 and / or the concentration of sulfur dioxide SO2 in a method for evaluating the effectiveness of a dechlorination process of a liquid.

Images