Indian Patents. 214937:AN IMPROVED ELECTROLYTE USEFUL FOR DETECTION AND DETERMINATION OF GASES PRESENT IN A GAS STREAM

Title of Invention	AN IMPROVED ELECTROLYTE USEFUL FOR DETECTION AND DETERMINATION OF GASES PRESENT IN A GAS STREAM
Abstract	An electrolyte composition useful for the detection and determination of gases, having reducing properties in gas streams which comprises potassium iodide in the range 3 to 6.0% by weight of the composition and a buffer in the range of 9 to 40.0% by weight, and the balance being water

Full Text	This invention relates to an electrolyte composition useful for detecting and determining the presence of gases having reducing properties in a gas stream. This invention particularly relates to an improved electrolyte useful for the detection and determination of the presence of gases such as SO , H S and CO having reducing properties in a gas stream. The 2 electrolyte of the present invention can also be used for the determination of the amount of such gases present in the process gas streams. Due to increased activity in the chemical industries for production of industrial chemicals there is a need for producing more and more reducing gases. The gases so produced are not completely utilised in the process and major part of such gases are released to the atmosphere causing air pollution problems. In addition process efficiency is also decreased. Hence it is very essential and important either to restrict the formation of such polluting gases or to monitor the formation of such gases to a certain limit and use in the process itself, thereby improving the efficiency of the process. Various methods such as Cou-lometry, spectrophotometry, thermal conductivity, pulse fluros-cense etc are used for the measurement of gases having reducing properties. Although various other methods such as spectrophotometry, thermal conductivity, pulse fluroscence etc are also used for the determination and detection of gases having reducing properties such as SO , the coulometric method is considered the most drift 2 free, wet chemical method and has less interference from other gases. Among the various methods Coulometric method is consid- ered as the most drift free, and has less interference from other gases. The other advantages of the coulometric technique are: * It is simple, accurate and low cost. * It is amenable for automation and measurement of high and low concentration. * It can give trouble free operation for long duration. * It does not require frequent calibration. The principle of coulometric technique has been employed for the determination of high as well as low (ppm) concentrations of gases having reducing properties such as SO gas in the process gas streams. Currently the presence of gases having reducing properties in gas streams is determined and/or detected using an electro¬chemical type gas analyser employing an electrolyte (composi¬tion) . Literature survey recommends a system based on Bro¬mine-Bromide electrolyte for the determination of gases having reducing properties in a gas stream at ppm/ppb level. The -6 concentration of Bromine used is of the order of 10 M. For determining high concentration of gases having reducing proper¬ty, the use of Bromine containing electrolyte is not suitable due to the loss of Bromine during estimation (due to its volatility) causing errors in measurement. Other type of electrolyte available for the determination of gases having reducing property such as SO is based on the use of Pyridine, Iodine and Methanol (Karl-Fischer type). Iodine is used as an oxidising agent and methanol as a solvent for iodine. Pyridine serves as a base to neutralise any acid formed during estimation. This electrolyte can be used for the determination of gases having reducing properties such as SO and not suitable for other gases such as H S, CO etc having reducing properties. The electrolyte containing pyridine has the following disadvan¬tages. 1. The presence of Pyridine present in the electrolyte gives a bad odour which is a undesirable. 2. The electrolyte is sensitive to excess moisture. Hence it reguires rest time (of upto 30 mts) in between succes¬ sive determinations. 3. The electrolyte has limited life expectancy and has to be changed every 24 hours. This will increase the cost of operation. 4. The cost of the solution is US$800 per litre. (Reguirement is 150mL per day) The presence of reducing gas in the gas stream is detected by passing the gas through the electrochemical type gas analyser incorporating the said electrolyte(composition). An embodiment of the electrochemical type analyser is shown in fig 1 of the drawing accompanying this specification. The analyser usually consists of a cell with two sets of elec¬trodes immersed in the electrolyte. One set of electrode called the sensing electrodes(l) measure the ratio of the constituents in the electrolyte solution in terms of micro-amps. The other set of electrodes called generating electrodes(2) through which DC current is passed to restore the original ratio of the constitu¬ents which gets altered by the passage of gas stream containing the gases having reducing properties. With ' L ' shaped platinum sensing electrodes, it is possible to measure the current generated due to particular constituents ratio present in the solution. The generator electrodes are also made of platinum and used for the restoration of the constituents ratio by electrolysis. In order to avoid error in the sensing current measurement due to the generation of hydrogen during electrolysis, the generator electrodes are separated using a sintered glass disc (3). The electrolyte present in the anode side is called the anolyte (4) and that in the cathode side is called the catholyte (5). The anolyte and catholyte may be the same or different. The sampled gas(7) or the standard gas from a cylinder(6) is taken through a peristaltic pump(17) where it is mixed with air from an aerator(8) and sent to the electrochemical by actuating a solenoid valve(14). When the gas is not passed through the elec¬trochemical cell it is bypassed to an alkali trap(9) by deener-gising the solenoid(14). The solenoid vales are energised or deenergised by means of solid state relays(13) from the electron¬ic unit(10). The sensing electrodes are interfaced to part 11 and the generator electrodes are interfaced to part 12 in the electronic unit. The electronic unit is interfaced to a Personal Computer(16). Different sections of the electronic unit(10 shown in Figl) are : 1. Milli volt signal conditioner (11) : - to measure the current from the sensing electrodes in terms of millivolts. 2. Milli Amp signal conditioner/generator (12) : - to generate and measure the current through generating electrodes. 3. Solid state relay interface: - to energise sole¬noids (14) to pass gas through the cell or to by pass gas through an alkali trap (9). 4. Power supply unit (15): - to provide power supply to various sections. PC system with interface card: A multifunction data acquisition card is used in an IBM compatible PC system to process the condi¬tioned signals in the measuring and generating electrodes and also to control the direction of flow of SO gas and to generate 2 appropriate current for electrolysis and finally to compute and display the SO concentration. 2 The system uses a peristaltic pump (17) to pass known volume of gas through the cell containing improved electrolyte. The principle by which the analyser functions to detect and determine the presence of gases having reducing property present in a gas stream is explained below. When a sample containing reducing properties such as SO gas 2 is allowed to react with the electrolyte, it alters the concen¬tration of the constituents present in the electrolyte which in turn decreases the observed current between the electrodes. The difference in current is sensed by the sensing electrodes. To avoid the drawbacks of the existing electrolyte useful for the detection and determination of gases having reducing properties in the gas stream and reducing the downtime of such detection and determination a need has arisen to provide an improved electrolyte for the purpose. Therefore the main objective of the present invention is to provide an improved electrolyte useful for the detection of gases having reducing properties present in process gas streams. Another objective of the present invention is to provide an improved electrolyte useful for determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can eliminate the use of pyridine and avoid bad odour; Yet another objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can measure the concentration of such gases present in the gas stream in the presence of moisture; One other objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can eliminate down time in between measurements; Another objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can be used over an extended period without the need for changing the elec¬trolyte; Still another objective of the present invention is to provide an improved electrolyte useful in detecting and deter- mining the presence of gases having reducing properties in proc¬ess gas streams employing the coulometric technique which can be used for detecting and determining gases having reducing proper¬ties at all concentrations. With the above objectives in view, we have initiated re¬search work to develop , an improved electrolyte which can be used for the detection and determination of the presence of gases having reducing properties in process streams employing coulomet¬ric technique. Initialy we thought of using Iodine-Iodide combination as electrolyte. Accordingly experiments were conducted by passing known quantities of standard gases having reducing properties such as SO gas through (Iodine - Iodide system) having good 2 conductivity. The use of the Iodine - Iodide electrolyte for continuous determination of gases having reducing properties such as SO at 10 % level generate sulphuric acid build-up in the 2 solution which lowers the pH of the medium. At low pH conditions, aerial oxidation of Iodide to Iodine takes place causing error in the detection and determination. Hence the medium requires a buffer to resist the acidity generated during each determinations. Some of the buffer systems which can be used are phosphoric acid, boric acid, phthalic acid and citric acid. The Iodine present in the electrolyte oxidises the gas having reducing properties and gets itself reduced to iodide ion. This reaction results in a reduction of a preset (sens¬ing) current generated between the sensing electrodes in the cell shown in fig 1 .The original (sensed) current, prior to passing of the gas stream containing gases having reducing properties such as S02 can be restored by electrolysis, which is effected by passing proportional current through the generating electrodes in the cell. The quantity of electricity (current * time) needed in the process of restoring to the original preset current, is a direct measure of the presence and the concentration of gas having reducing properties such as S02 that reduced the Iodine. The reaction in the cell can be explained by the chemical equation given below. (Equation Removed) A buffered solution is necessary to resist the change in pH due to the generation of sulphuric acid in the reaction, when a gas with reducing property like S02 at 10% concentration level is measured continuously. The use of buffer solution also avoids frequent changing of the electrolyte solution. Accordingly the present invention accordingly provides an electrolyte composition useful for the detection and determination of gases, having reducing properties in gas streams which comprises potassium iodide in the range 3 to 6.0% by weight of the composition and a buffer/in the range of 9 to 40.0% by weight, and the balance being water. The composition obtained by the process of the present invention is neither a product of chemical reaction nor a mere admixture but is a synergistic formulation having properties different than the aggregate properties of the individual components. No chemical reaction between the constituents of the said composition. According to an embodiment of the present invention, the present electrolyte comprises an aqueous solution consisting of Potassium Iodide 3.5% by weight of the composition Disodium hydrogen phosphate 10.5% by weight of the composition Citric acid 7% by weight of the composition pH of the combination buffer 5 + 0.1% The electrolytes of the present invention were tested for the detection and determination of gases having reducing proper¬ty. It is observed that the above mentioned electrolyte (150mL) was found to be useful for the determination of pure SO gas (a 2 gas with reducing property) upto 300mL with a change of pH within 0.5 units from the initial pH of the electrolyte. The following experiments describe in detail the inven¬tion which are provided to illustrate the invention and should not be construed to limit the scope of the invention. Example 1 : An aqueous solution of the electrolyte having the following composition was prepared for laboratory trials for the determina- tion of SO gas concentration by using the components 2 Potassium Iodide (KI) 3 % by wt Disodiumhydrogenphosphate 20% by wt pH of the solution 5.0 The above electrolyte (150mL) was filled into the anode compartment ( 4 ) and 50mL into the cathode compartment ( 5 ). Ini- tially 150mA of current was passed through the generating elec¬trodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO 2 gas with reducing properties contained in a gas cylinder having 99.99% purity. The SO gas cylinder was connected to the peristaltic pump(f)M 2 ' with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from the aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was bypassed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit, ie the sensing current decreases from 6 uA to a lower value. This indicates the presence of reducing gas in the gas (in this case S02) being passed. A DC current(150mA ie ri' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas present in the gas being sam¬pled. From the guantity of electricity ('!' * 't' coulombs) passed through the generating electrodes, the concentration of the reducing (SO ) gas was computed. 5 trials were done for the determination of SO gas in the 2 sample and each time restoring the cell to Starting mode before the passage of next sample. The results are tabulated in Table 1. Column 1 in the table represent the time (in Hours & Minutes) and column 2 represent the concentration in mL. Since the SO gas(99.99% purity) was 2 passed from a standard cylinder for 60 seconds and the peristal¬tic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%. Table 1: (Table Removed) It is evident from the table 1 that 1) The repeatability of the value of SO concentration indicate the precision of measurement; 2) and there is no down time between measurements. Example 2: Aqueous solution of the electrolyte having the following compo¬sition was prepared for the laboratory trials for the determina¬tion of SO concentration. Potassium Iodide 5% by Wt Citric acid 20% by Wt Disodiumhydrogenphosphate 5% by Wt pH of the solution 5.0 The above electrolyte(150mL) was filled into the anode compartment (4) and 50mL into the cathode compartment (5). Ini¬tially 150mA of current was passed through the generating elec¬trolytes in the anode compartment till the sensing electrodes measure a current of 6 uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO 2 gas with reducing properties contained in a gas cylinder having 99.99% purity. The SO gas cylinder was connected to the peristaltic pump 2 with a pumping speed set to 2.50mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This indicates the presence of reducing gas SO present in the gas be- ing passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concen¬tration of the reducing gas that was sampled. From the guantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO 2 gas was computed. 5 trials were done for the determination of SO gas in the sample and restoring the cell to Starting mode before the passage of next sample. The results are tabulated in Table 2. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in mL. Since the SO gas(99.99% purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 2.50mL/min the expected computed concentration was to be around 2.50mL or 99.99%. Table 2: (Table Removed0) It is evident from the table 2 that 1) The repeatability of the value of SO concentration indicate the precision of measurement; 2) and there is no down time between measurements Example 3: Yet another aqueous solution of the electrolyte having the fol¬lowing composition was prepared for the laboratory trials for the determination of SO gas concentration. (Table Removed) The above electrolyte(150mL) was filled into the anode compartment(4) and 50mL into the cathode compartment(5). Ini¬tially 150mA of current was passed through the generating elec¬trolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO 2 gas with reducing properties contained in a gas cylinder having 99.99% purity. The SO gas cylinder was connected to the peristaltic pump 2 with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('f seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas present in the gas passed. From the guantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO2 gas was computed. 5 trials were done for the determination of SO2 gas in the sample and each time restoring the cell to Starting mode before the passage of next sample. The results are tabulated in Table 2. The columnl in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in mL. Since the SO gas(99.99% purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%. Table 3: (Table Removed) It is evident from the table 3 that 1) The repeatability of the experiment indicate the precision of measurement; 2) and there is no down time between measurements Example 4 The electrolyte of the present invention described in the example 1 consisting of Potassium Iodide (KI) 3 % by wt Disodiumhydrogenphosphate 20% by wt pH of the solution 5.0 was used for the determination of SO gas concentration in a sulphuric acid plant. The process SO gas stream in moisture from stage I of the vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10. OOmL/min. The gas coining out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 5 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current will decrease from 6uA to a lower value. This indicates the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled. From the quantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO 2 gas was computed. 5 trials were done for the determination of SO gas in the 2 sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 9.1 ± 0.2%. The results obtained were comparable to that obtained by the instrumental method. The results are tabulated in Table 4. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 4: (Table Removed) It is evident from the table 4 that 1) The repeatability of the experiment indicate the precision of measurement; 2) The electrolyte could be used for the detect and determine of the gas concentration in the presence of moisture; and 3) there is no down time between measurements Example 5 The electrolyte described in the example 2 consisting of Potassium Iodide (KI) 5 % by wt Citric acid 20% by wt Disodiumhydrogenphosphate 5% by wt pH of the solution 5.0 was used for the determination of SO gas concentration in a sulphuric acid plant. The above electrolyte(150mL) was filled into the anode compartment(4) and 50mL into the cathode compartment(5).Ini¬ tially 150mA of current was passed through the generating elec- trolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO gas with reducing properties contained in a gas cylinder having 99.99% purity. The process SO gas stream in moisture from stage II of the vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10.OOmL/min. The gas coining out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 5 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('f seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled. From the quantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO gas was computed. 5 trials were done for the determination of SO gas in the sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 6.00 ± 0.15%. The results are tabulated in Table4. The columnl in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 5: (Table Removed) It is inferred from the table5 that 1) The repeatability of the experiments indicate the precision of measurement; 2) The electrolyte could be used to detect and determine the gas concentration in the presence of moisture; 3) and there is no down time between measurements Example 6 The electrolyte described in the experiment, consisting of Potassium Iodide (KI) 4 % by wt Citric acid 10% by wt Disodiumhydrogenphosphate 20% by wt pH of the solution 5.0 was tested in a sulphuric acid plant. The electrolyte(150mL) was filled into the anode compart¬ment (4) and 50mL into the cathode compartment(5). Initially 150mA of current was passed through the generating electrolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO gas 2 with reducing properties contained in a gas cylinder having 99.99% purity. The stack gas in the sulphuric acid plant was connected to the peristaltic pump with a pumping speed set to lOOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 20 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 20 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 20 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decrease from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled. From the quantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO gas was computed. 5 trials were done for the determination of SO gas in the sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 0.031 + 0.002%. The results are tabulated in Table 6. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 6: (Table Removed) It is inferred from the table 6 that 1) The repeatability of the experiments indicate the precision of measurement; 2) The electrolyte could be used for detect and determine the gas concentration in the presence of moisture; and 3) there is no down time between measurements. Example 7: The electrolyte described in the experiments consisting of Potassium Iodide (KI) 4 % by wt Citric acid 10% by wt Disodlumhydrogenphosphate 20% by wt pH of the solution 5.0 was used for the detection of H S gas concentration near a swew- age pumping station near Madras. The above electrolyte(150mL) was filled into the anode compartment(4) and 50mL into the cathode compartment(5). Initial¬ly 150mA of current was passed through the generating elec¬trodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO gas with reducing properties contained in a gas cylinder having 99.99% purity. The stack gas in the sulphuric acid plant was connected to the peristaltic pump with a pumping speed set to lOOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 10 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 10 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 10 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled. From the quantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO 2 gas was computed. 5 trials were done for the determination of SO gas in the sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in 1% Zinc acetate solution followed by lodimetric method(ie volumetric) and were found to be of the order of 1.52 ± 0.02%. The results are tabulated in Table 7. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 7: (Table Removed) It is inferred from the table 7 that 1) The repeatability of the experiment indicate the precision of measurement; 2) The electrolyte could be used for detect and determine the H S gas concentration in the presence of moisture; and 3) there is no down time between measurements. Example 8: In the laboratory a comparison study was made for the deter¬mination of SO gas with the use of electrolyte based on pyri- dine, iodine and dry methanol (a commercial product costing $800 per litre). 150 ml of the electrolyte based on pyridine, iodine and dry methanol(imported sample) was used in the anode compart¬ment of the cell and 50 ml electrolyte based on phosphoric acid(imported) was used in the cathode compartment. Initially 150mA of current was passed through the generating electrodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO gas with reducing properties contained in a gas cylinder having 99.99% purity. The standard SO gas (99.99% purity) from a cylinder was connected to the peristaltic pump with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(S) and was allowed to pass to the anode compartment of the electrochemical cell for 60 seconds by ener¬gising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dis¬solved. While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled. From the quantity of electricity ('i' * 't' coulombs) passed through the generating electrodes, the concentration of the SO gas was computed. 5 trials were done for the determination of SO gas in the sample and each time restoring the cell to Starting mode before the passage of next sample. The results are tabulated in Table 7. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in mL. Since the SO gas(99.99% purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%. Table 8: (Table Removed) It is evident from the table 8 that the repeatability of the value of SO concentration indicate the precision of measurement using pyridine based system. However the main draw back was that it required a minimum of 30 minutes of wait time between deter-minations . Example 9: A field study was conducted in a sulphuric acid plant with the use of electrolyte based on pyridine, iodine and dry methanol (a commercial product costing $800 per litre) for the detection and determination of SO gas. 150 ml of the electrolyte based on pyridine, iodine and dry methanol(imported sample) was used in the anode compartment of the cell and 50 ml electrolyte based on phosphoric acid(imported) was used in the cathode compartment. Initially 150mA of current was passed through the generating electrodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO gas with reducing properties contained in a gas cylinder having 99.99% purity. The process SO gas stream in moisture from stage I of the vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10.OOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved. While the gas was passed through the cell for 5 minutes, due to the presence of moisture in the gas stream, erratic change in the sensing current was observed and the electrolyte ultimately failed to respond to the detection of the SO gas even though the experiment was repeated several times. Hence it was inferred that when this solution was tested for the determination of SO in the sulphuric acid plant, the solution failed due to the presence of moisture in the gas sample. This electrolyte based on pyridine is sensitive to moisture and hence it is not suitable for industry environment. Advantages of the present invention. 1) The repeatability of the experiments indicates the precision of measurement; 2) The electrolyte could even detect and determine the presence of reducing gases in the presence of moisture; 3) There is no down time in between measurements 4) Useful for on-line measurement even in the industrial envi- ronment. It is not sensitive to moisture and therefore also be used for detecting and monitoring with industrial process. The major drawback in the pyridine based electrolyte is that it is sensitive to moisture and it is based on non aqueous solvent. Hence it is not suitable in the industrial process gas monitoring in the presence of moisture. 1. An electrolyte composition useful for the detection and determination of gases, having reducing properties in gas streams which comprises potassium iodide in the range 3 to 6.0% by weight of the composition and a buffer/in the range of 9 to 40.0% by weight, and the balance being water. 2. An electrolyte composition as claimed in claim 1 wherein the buffer used is selected from Phosphoric Acid, Boric Acid, Citric Acid, Succinic Acid, Di Sodium Hydrogen Phosphate, Mono Sodium Hydrogen Phosphate or mixtures thereof. 3. An electrolyte composition claimed in claims 1 to 2 wherein the amount of potassium iodide is 3% by weight, buffer 20% by weight and the pH of the electrolyte being 4.5 to 5.1. 4. An electrolyte composition useful for the detection and determination of gases having reducing properties present in process gas streams substantially as herein described with reference to the examples.

Full Text

This invention relates to an electrolyte composition useful for detecting and determining the presence of gases having reducing properties in a gas stream. This invention particularly relates to an improved electrolyte useful for the detection and determination of the presence of gases such as SO , H S and CO having reducing properties in a gas stream. The 2 electrolyte of the present invention can also be used for the determination of the amount of such gases present in the process gas streams.
Due to increased activity in the chemical industries for production of industrial chemicals there is a need for producing more and more reducing gases. The gases so produced are not completely utilised in the process and major part of such gases are released to the atmosphere causing air pollution problems. In addition process efficiency is also decreased. Hence it is very essential and important either to restrict the formation of such polluting gases or to monitor the formation of such gases to a certain limit and use in the process itself, thereby improving the efficiency of the process. Various methods such as Cou-lometry, spectrophotometry, thermal conductivity, pulse fluros-cense etc are used for the measurement of gases having reducing properties.
Although various other methods such as spectrophotometry, thermal conductivity, pulse fluroscence etc are also used for the determination and detection of gases having reducing properties
such as SO , the coulometric method is considered the most drift 2
free, wet chemical method and has less interference from other gases. Among the various methods Coulometric method is consid-

ered as the most drift free, and has less interference from other
gases.
The other advantages of the coulometric technique are:
* It is simple, accurate and low cost.
* It is amenable for automation and measurement of high
and low concentration.
* It can give trouble free operation for long duration.
* It does not require frequent calibration.
The principle of coulometric technique has been employed for the determination of high as well as low (ppm) concentrations of
gases having reducing properties such as SO gas in the process
gas streams.
Currently the presence of gases having reducing properties in gas streams is determined and/or detected using an electro¬chemical type gas analyser employing an electrolyte (composi¬tion) . Literature survey recommends a system based on Bro¬mine-Bromide electrolyte for the determination of gases having
reducing properties in a gas stream at ppm/ppb level. The
-6 concentration of Bromine used is of the order of 10 M. For
determining high concentration of gases having reducing proper¬ty, the use of Bromine containing electrolyte is not suitable due to the loss of Bromine during estimation (due to its volatility) causing errors in measurement.
Other type of electrolyte available for the determination
of gases having reducing property such as SO is based on the use
of Pyridine, Iodine and Methanol (Karl-Fischer type). Iodine is used as an oxidising agent and methanol as a solvent for iodine.
Pyridine serves as a base to neutralise any acid formed during estimation. This electrolyte can be used for the determination of
gases having reducing properties such as SO and not suitable for
other gases such as H S, CO etc having reducing properties.
The electrolyte containing pyridine has the following disadvan¬tages.
1. The presence of Pyridine present in the electrolyte gives a
bad odour which is a undesirable.
2. The electrolyte is sensitive to excess moisture. Hence
it reguires rest time (of upto 30 mts) in between succes¬
sive determinations.
3. The electrolyte has limited life expectancy and has to
be changed every 24 hours. This will increase the cost
of operation.
4. The cost of the solution is US$800 per litre. (Reguirement
is 150mL per day)
The presence of reducing gas in the gas stream is detected by passing the gas through the electrochemical type gas analyser incorporating the said electrolyte(composition).
An embodiment of the electrochemical type analyser is shown in fig 1 of the drawing accompanying this specification. The analyser usually consists of a cell with two sets of elec¬trodes immersed in the electrolyte. One set of electrode called the sensing electrodes(l) measure the ratio of the constituents in the electrolyte solution in terms of micro-amps. The other set of electrodes called generating electrodes(2) through which DC current is passed to restore the original ratio of the constitu¬ents which gets altered by the passage of gas stream containing
the gases having reducing properties.
With ' L ' shaped platinum sensing electrodes, it is possible to measure the current generated due to particular constituents ratio present in the solution. The generator electrodes are also made of platinum and used for the restoration of the constituents ratio by electrolysis. In order to avoid error in the sensing current measurement due to the generation of hydrogen during electrolysis, the generator electrodes are separated using a sintered glass disc (3). The electrolyte present in the anode side is called the anolyte (4) and that in the cathode side is called the catholyte (5). The anolyte and catholyte may be the same or different.
The sampled gas(7) or the standard gas from a cylinder(6) is taken through a peristaltic pump(17) where it is mixed with air from an aerator(8) and sent to the electrochemical by actuating a solenoid valve(14). When the gas is not passed through the elec¬trochemical cell it is bypassed to an alkali trap(9) by deener-gising the solenoid(14). The solenoid vales are energised or deenergised by means of solid state relays(13) from the electron¬ic unit(10). The sensing electrodes are interfaced to part 11 and the generator electrodes are interfaced to part 12 in the electronic unit. The electronic unit is interfaced to a Personal Computer(16). Different sections of the electronic unit(10 shown in Figl) are :
1*. Milli volt signal conditioner (11) : - to measure the current from the sensing electrodes in terms of millivolts.
2*. Milli Amp signal conditioner/generator (12) : - to generate and measure the current through generating electrodes.
3*. Solid state relay interface: - to energise sole¬noids (14) to pass gas through the cell or to by pass gas through an alkali trap (9).
4*. Power supply unit (15): - to provide power supply to various sections.
PC system with interface card: A multifunction data acquisition card is used in an IBM compatible PC system to process the condi¬tioned signals in the measuring and generating electrodes and
also to control the direction of flow of SO gas and to generate
2
appropriate current for electrolysis and finally to compute and
display the SO concentration. 2
The system uses a peristaltic pump (17) to pass known volume of gas through the cell containing improved electrolyte.
The principle by which the analyser functions to detect and determine the presence of gases having reducing property present in a gas stream is explained below.
When a sample containing reducing properties such as SO gas
2
is allowed to react with the electrolyte, it alters the concen¬tration of the constituents present in the electrolyte which in turn decreases the observed current between the electrodes. The difference in current is sensed by the sensing electrodes.
To avoid the drawbacks of the existing electrolyte useful for the detection and determination of gases having reducing properties in the gas stream and reducing the downtime of such detection and determination a need has arisen to provide an improved electrolyte for the purpose.
Therefore the main objective of the present invention is to provide an improved electrolyte useful for the detection of gases having reducing properties present in process gas streams.
Another objective of the present invention is to provide an improved electrolyte useful for determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can eliminate the use of pyridine and avoid bad odour;
Yet another objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can measure the concentration of such gases present in the gas stream in the presence of moisture;
One other objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can eliminate down time in between measurements;
Another objective of the present invention is to provide an improved electrolyte useful for detecting and determining the presence of gases having reducing properties in process gas streams employing the coulometric technique which can be used over an extended period without the need for changing the elec¬trolyte;
Still another objective of the present invention is to provide an improved electrolyte useful in detecting and deter-
mining the presence of gases having reducing properties in proc¬ess gas streams employing the coulometric technique which can be used for detecting and determining gases having reducing proper¬ties at all concentrations.
With the above objectives in view, we have initiated re¬search work to develop , an improved electrolyte which can be used for the detection and determination of the presence of gases having reducing properties in process streams employing coulomet¬ric technique.
Initialy we thought of using Iodine-Iodide combination as electrolyte. Accordingly experiments were conducted by passing known quantities of standard gases having reducing properties
such as SO gas through (Iodine - Iodide system) having good 2
conductivity. The use of the Iodine - Iodide electrolyte for continuous determination of gases having reducing properties such
as SO at 10 % level generate sulphuric acid build-up in the 2
solution which lowers the pH of the medium. At low pH conditions, aerial oxidation of Iodide to Iodine takes place causing error in the detection and determination. Hence the medium requires a buffer to resist the acidity generated during each determinations. Some of the buffer systems which can be used are phosphoric acid, boric acid, phthalic acid and citric acid.
The Iodine present in the electrolyte oxidises the gas having reducing properties and gets itself reduced to iodide ion. This reaction results in a reduction of a preset (sens¬ing) current generated between the sensing electrodes in the cell shown in fig 1 .The original (sensed) current, prior to passing of the gas stream containing gases having reducing properties such as S02 can be restored by electrolysis, which is effected by passing proportional current through the generating electrodes in the cell.
The quantity of electricity (current * time) needed in the process of restoring to the original preset current, is a direct measure of the presence and the concentration of gas having reducing properties such as S02 that reduced the Iodine.
The reaction in the cell can be explained by the chemical equation given below.
(Equation Removed)
A buffered solution is necessary to resist the change in pH due to the generation of sulphuric acid in the reaction, when a gas with reducing property like S02 at 10% concentration level is measured continuously. The use of buffer solution also avoids frequent changing of the electrolyte solution.
Accordingly the present invention accordingly provides an electrolyte composition useful for the detection and determination of gases, having reducing properties in gas streams which comprises potassium iodide in the range 3 to 6.0% by weight of the composition and a buffer/in the range of 9 to 40.0% by weight, and the balance being water.
The composition obtained by the process of the present invention is neither a product of chemical reaction nor a mere admixture but is a synergistic formulation having properties different than the aggregate properties of the individual components. No chemical reaction between the constituents of the said composition.
According to an embodiment of the present invention, the present electrolyte comprises an aqueous solution consisting of
Potassium Iodide 3.5% by weight of the composition
Disodium hydrogen phosphate 10.5% by weight of the composition
Citric acid 7% by weight of the composition
pH of the combination buffer 5 + 0.1%
The electrolytes of the present invention were tested for the detection and determination of gases having reducing proper¬ty. It is observed that the above mentioned electrolyte (150mL)
was found to be useful for the determination of pure SO gas (a
2
gas with reducing property) upto 300mL with a change of pH within 0.5 units from the initial pH of the electrolyte.
The following experiments describe in detail the inven¬tion which are provided to illustrate the invention and should not be construed to limit the scope of the invention. Example 1 :
An aqueous solution of the electrolyte having the following composition was prepared for laboratory trials for the determina-
tion of SO gas concentration by using the components 2
Potassium Iodide (KI) 3 % by wt
Disodiumhydrogenphosphate 20% by wt
pH of the solution 5.0
The above electrolyte (150mL) was filled into the anode
compartment ( 4 ) and 50mL into the cathode compartment ( 5 ). Ini-

tially 150mA of current was passed through the generating elec¬trodes in the anode compartment till the sensing electrodes
measure a current of 6uA in the display unit. Now the cell is
ready (Starting Mode) for the detection and determination of SO
2
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The SO gas cylinder was connected to the peristaltic pump(f)M
2 '
with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from the aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was bypassed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit, ie the sensing current decreases from 6 uA to a lower value. This indicates the presence of reducing gas in the gas (in this case S02) being passed. A DC current(150mA ie ri' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas present in the gas being sam¬pled.
From the guantity of electricity ('!' * 't' coulombs) passed through the generating electrodes, the concentration of the
reducing (SO ) gas was computed.

5 trials were done for the determination of SO gas in the
2
sample and each time restoring the cell to Starting mode before the passage of next sample.
The results are tabulated in Table 1. Column 1 in the table represent the time (in Hours & Minutes) and column 2 represent
the concentration in mL. Since the SO gas(99.99% purity) was
2
passed from a standard cylinder for 60 seconds and the peristal¬tic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%. Table 1:
(Table Removed)
It is evident from the table 1 that
1) The repeatability of the value of SO concentration indicate
the precision of measurement;
2) and there is no down time between measurements.
Example 2:
Aqueous solution of the electrolyte having the following compo¬sition was prepared for the laboratory trials for the determina¬tion of SO concentration.
Potassium Iodide 5% by Wt
Citric acid 20% by Wt
Disodiumhydrogenphosphate 5% by Wt
pH of the solution 5.0
The above electrolyte(150mL) was filled into the anode compartment (4) and 50mL into the cathode compartment (5). Ini¬tially 150mA of current was passed through the generating elec¬trolytes in the anode compartment till the sensing electrodes measure a current of 6 uA in the display unit. Now the cell is
ready (Starting Mode) for the detection and determination of SO
2
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The SO gas cylinder was connected to the peristaltic pump 2
with a pumping speed set to 2.50mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This
indicates the presence of reducing gas SO present in the gas be-
ing passed. A DC current(150mA ie 'i' Amps) was passed through
the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concen¬tration of the reducing gas that was sampled.
From the guantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
2
gas was computed.
5 trials were done for the determination of SO gas in the
sample and restoring the cell to Starting mode before the passage of next sample.
The results are tabulated in Table 2. The column 1 in the table represent the time (in Hours & Minutes) and the column 2
represent the concentration in mL. Since the SO gas(99.99%
purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 2.50mL/min the expected computed concentration was to be around 2.50mL or 99.99%.
Table 2:
(Table Removed0)
It is evident from the table 2 that
1) The repeatability of the value of SO concentration indicate
the precision of measurement;
2) and there is no down time between measurements
Example 3:
Yet another aqueous solution of the electrolyte having the fol¬lowing composition was prepared for the laboratory trials for the
determination of SO gas concentration.
(Table Removed)
The above electrolyte(150mL) was filled into the anode compartment(4) and 50mL into the cathode compartment(5). Ini¬tially 150mA of current was passed through the generating elec¬trolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is
ready (Starting Mode) for the detection and determination of SO
2
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The SO gas cylinder was connected to the peristaltic pump 2
with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(8) and was allowed to pass to the anode compartment of the electrochemi¬cal cell for 60 seconds by energising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic pump to the cell. After passing
the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('f seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas present in the gas passed.
From the guantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO2
gas was computed.
5 trials were done for the determination of SO2 gas in the
sample and each time restoring the cell to Starting mode before the passage of next sample.
The results are tabulated in Table 2. The columnl in the table represent the time (in Hours & Minutes) and the column 2
represent the concentration in mL. Since the SO gas(99.99%
purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%.

Table 3:
(Table Removed)
It is evident from the table 3 that
1) The repeatability of the experiment indicate the precision of
measurement;
2) and there is no down time between measurements
Example 4
The electrolyte of the present invention described in the example 1 consisting of
Potassium Iodide (KI) 3 % by wt
Disodiumhydrogenphosphate 20% by wt
pH of the solution 5.0
was used for the determination of SO gas concentration in a
sulphuric acid plant.
The process SO gas stream in moisture from stage I of the
vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10. OOmL/min. The gas coining out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid
valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 5 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current will decrease from 6uA to a lower value. This indicates the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled.
From the quantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
2
gas was computed.
5 trials were done for the determination of SO gas in the
2
sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 9.1 ± 0.2%. The results obtained were comparable to that obtained by the instrumental method.
The results are tabulated in Table 4. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %.
Table 4:
(Table Removed)
It is evident from the table 4 that
1) The repeatability of the experiment indicate the precision of
measurement;
2) The electrolyte could be used for the detect and determine of
the gas concentration in the presence of moisture; and
3) there is no down time between measurements
Example 5
The electrolyte described in the example 2 consisting of
Potassium Iodide (KI) 5 % by wt
Citric acid 20% by wt
Disodiumhydrogenphosphate 5% by wt
pH of the solution 5.0
was used for the determination of SO gas concentration in a
sulphuric acid plant.
The above electrolyte(150mL) was filled into the anode
compartment(4) and 50mL into the cathode compartment(5).Ini¬
tially 150mA of current was passed through the generating elec-
trolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is
ready (Starting Mode) for the detection and determination of SO
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The process SO gas stream in moisture from stage II of the
vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10.OOmL/min. The gas coining out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 5 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('f seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled.
From the quantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
gas was computed.
5 trials were done for the determination of SO gas in the
sample and each time restoring the cell to Starting mode before
the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 6.00 ± 0.15%.
The results are tabulated in Table4. The columnl in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 5:
(Table Removed)
It is inferred from the table5 that
1) The repeatability of the experiments indicate the precision of
measurement;
2) The electrolyte could be used to detect and determine the gas
concentration in the presence of moisture;
3) and there is no down time between measurements
Example 6
The electrolyte described in the experiment, consisting of
Potassium Iodide (KI) 4 % by wt
Citric acid 10% by wt
Disodiumhydrogenphosphate 20% by wt
pH of the solution 5.0
was tested in a sulphuric acid plant.
The electrolyte(150mL) was filled into the anode compart¬ment (4) and 50mL into the cathode compartment(5). Initially 150mA of current was passed through the generating electrolytes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready
(Starting Mode) for the detection and determination of SO gas
2
with reducing properties contained in a gas cylinder having 99.99% purity.
The stack gas in the sulphuric acid plant was connected to the peristaltic pump with a pumping speed set to lOOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 20 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 20 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 20 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decrease from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled.

From the quantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
gas was computed.
5 trials were done for the determination of SO gas in the
sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in Sodiumhydroxide solution followed by lodimetric method(ie volumetric) and were found to be of the order of 0.031 + 0.002%.
The results are tabulated in Table 6. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 6:
(Table Removed)
It is inferred from the table 6 that
1) The repeatability of the experiments indicate the precision of
measurement;
2) The electrolyte could be used for detect and determine the
gas concentration in the presence of moisture; and
3) there is no down time between measurements.
Example 7:
The electrolyte described in the experiments consisting of
Potassium Iodide (KI) 4 % by wt
Citric acid 10% by wt
Disodlumhydrogenphosphate 20% by wt
pH of the solution 5.0
was used for the detection of H S gas concentration near a swew-
age pumping station near Madras.
The above electrolyte(150mL) was filled into the anode compartment(4) and 50mL into the cathode compartment(5). Initial¬ly 150mA of current was passed through the generating elec¬trodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is
ready (Starting Mode) for the detection and determination of SO
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The stack gas in the sulphuric acid plant was connected to the peristaltic pump with a pumping speed set to lOOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 10 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 10 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 10 minutes, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This
is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled.
From the quantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
2
gas was computed.
5 trials were done for the determination of SO gas in the
sample and each time restoring the cell to Starting mode before the passage of next sample. The process gas samples were also analysed after fixing it in 1% Zinc acetate solution followed by lodimetric method(ie volumetric) and were found to be of the order of 1.52 ± 0.02%.
The results are tabulated in Table 7. The column 1 in the table represent the time (in Hours & Minutes) and the column 2 represent the concentration in %. Table 7:
(Table Removed)
It is inferred from the table 7 that
1) The repeatability of the experiment indicate the precision
of measurement;
2) The electrolyte could be used for detect and determine the H S
gas concentration in the presence of moisture; and
3) there is no down time between measurements.
Example 8:
In the laboratory a comparison study was made for the deter¬mination of SO gas with the use of electrolyte based on pyri-
dine, iodine and dry methanol (a commercial product costing $800 per litre). 150 ml of the electrolyte based on pyridine, iodine and dry methanol(imported sample) was used in the anode compart¬ment of the cell and 50 ml electrolyte based on phosphoric acid(imported) was used in the cathode compartment. Initially 150mA of current was passed through the generating electrodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready
(Starting Mode) for the detection and determination of SO gas
with reducing properties contained in a gas cylinder having 99.99% purity.
The standard SO gas (99.99% purity) from a cylinder was
connected to the peristaltic pump with a pumping speed set to 1.25mL/min. The gas coming out of the peristaltic pump was mixed with air from an aerator(S) and was allowed to pass to the anode compartment of the electrochemical cell for 60 seconds by ener¬gising the solenoid valve(14) from the electronic unit. The air was mixed only to carry the gas coming out of the peristaltic
pump to the cell. After passing the gas for 60 seconds through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dis¬solved.
While the gas was passed through the cell for 60 seconds, a decrease in sensing current was observed in the display unit. ie the sensing current decreases from 6uA to a lower value. This is the detection of the presence of reducing gas being passed. A DC current(150mA ie 'i' Amps) was passed through the generating electrodes for a particular duration ('t' seconds) till the original sensing current of 6uA was restored. The time taken to restore the sensing current is a measure of the concentration of the reducing gas that was sampled.
From the quantity of electricity ('i' * 't' coulombs) passed
through the generating electrodes, the concentration of the SO
gas was computed.
5 trials were done for the determination of SO gas in the
sample and each time restoring the cell to Starting mode before the passage of next sample.
The results are tabulated in Table 7. The column 1 in the table represent the time (in Hours & Minutes) and the column 2
represent the concentration in mL. Since the SO gas(99.99%
purity) was passed from a standard cylinder for 60 seconds and the peristaltic pump being set to a flow rate of 1.25mL/min the expected computed concentration was to be around 1.25mL or 99.99%.
Table 8:
(Table Removed)
It is evident from the table 8 that the repeatability of the
value of SO concentration indicate the precision of measurement
using pyridine based system. However the main draw back was that it required a minimum of 30 minutes of wait time between deter-minations . Example 9:
A field study was conducted in a sulphuric acid plant with the use of electrolyte based on pyridine, iodine and dry methanol (a commercial product costing $800 per litre) for the detection
and determination of SO gas. 150 ml of the electrolyte based on
pyridine, iodine and dry methanol(imported sample) was used in the anode compartment of the cell and 50 ml electrolyte based on phosphoric acid(imported) was used in the cathode compartment. Initially 150mA of current was passed through the generating electrodes in the anode compartment till the sensing electrodes measure a current of 6uA in the display unit. Now the cell is ready (Starting Mode) for the detection and determination of SO
gas with reducing properties contained in a gas cylinder having 99.99% purity.
The process SO gas stream in moisture from stage I of the
vanadiumpentoxide bed was connected to the peristaltic pump with a pumping speed set to 10.OOmL/min. The gas coming out of the peristaltic pump was allowed to pass to the anode compartment of the electrochemical cell for 5 minutes by energising the solenoid valve(14) from the electronic unit. After passing the gas for 5 minutes through the cell, the gas was by passed by de-energising the solenoid valve to pass into an alkali trap(9) where the gas gets dissolved.
While the gas was passed through the cell for 5 minutes, due to the presence of moisture in the gas stream, erratic change in the sensing current was observed and the electrolyte ultimately
failed to respond to the detection of the SO gas even though the
experiment was repeated several times. Hence it was inferred
that when this solution was tested for the determination of SO
in the sulphuric acid plant, the solution failed due to the presence of moisture in the gas sample. This electrolyte based on pyridine is sensitive to moisture and hence it is not suitable for industry environment. Advantages of the present invention.
1) The repeatability of the experiments indicates the precision
of measurement;
2) The electrolyte could even detect and determine the presence
of reducing gases in the presence of moisture;

3) There is no down time in between measurements
4) Useful for on-line measurement even in the industrial envi-
ronment.
It is not sensitive to moisture and therefore also be used for
detecting and monitoring with industrial process.
The major drawback in the pyridine based electrolyte is that it
is sensitive to moisture and it is based on non aqueous solvent.
Hence it is not suitable in the industrial process gas monitoring
in the presence of moisture.

1. An electrolyte composition useful for the detection and determination of gases,
having reducing properties in gas streams which comprises potassium iodide in
the range 3 to 6.0% by weight of the composition and a buffer/in the range of 9
to 40.0% by weight, and the balance being water.
2. An electrolyte composition as claimed in claim 1 wherein the buffer used is
selected from Phosphoric Acid, Boric Acid, Citric Acid, Succinic Acid, Di Sodium
Hydrogen Phosphate, Mono Sodium Hydrogen Phosphate or mixtures thereof.
3. An electrolyte composition claimed in claims 1 to 2 wherein the amount of
potassium iodide is 3% by weight, buffer 20% by weight and the pH of the
electrolyte being 4.5 to 5.1.
4. An electrolyte composition useful for the detection and determination of gases
having reducing properties present in process gas streams substantially as herein
described with reference to the examples.

Documents:

2266-del-1996-abstract.pdf

2266-del-1996-claims.pdf

2266-del-1996-correspondence-others.pdf

2266-del-1996-correspondence-po.pdf

2266-del-1996-description (complete).pdf

2266-del-1996-drawings.pdf

2266-del-1996-form-1.pdf

2266-del-1996-form-19.pdf

2266-del-1996-form-2.pdf

2266-del-1996-form-4.pdf

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Patent Number

214937

Indian Patent Application Number

2266/DEL/1996

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

18-Feb-2008

Date of Filing

18-Oct-1996

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001,INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DR.NATESHAN BALASUBRAMANIAN, ASSOCIATE PROFESSOR	DEPT.OF CHEMISTRY, INDIAN INSTITUTE OF TECHNOLOGY, MADARAS-600036
2	MR.THOPPUR RAJAGOPAL NATRAJAN, SCIENTIST E II	CENTRAL SCIENTIFIC INSTRUMENTS ORGANISATION, MADRAS CENTRE, CSIR MADRAS COMPLEX, TARAMANI, MADRAS-600036.
3	DR. RANGASWAMI RAGHUNATHAN, SCIENTIST C	CENTRAL SCIENTIFIC INSTRUMENTS ORGANISATION, MADRAS CENTRE, CSIR MADRAS COMPLEX, TARAMANI, MADRAS.
4	MS. HEMAMALINI KASTHURI, TECHNICAL OFFICER B	CENTRAL SCIENTIFIC INSTRUMENTS ORGANISATION, MADRAS CENTRE, CSIR MADRAS COMPLEX, TARAMANI, MADRAS.
5	MS.VASANTHA BALASUBRAMANIAN, TECHNICAL OFFICER B	CENTRAL SCIENTIFIC INSTRUMENTS ORGANISATION, MADRAS CENTRE, CSIR MADRAS COMPLEX, TARAMANI, MADRAS.
6	MR. KRISHNAN SUNDARARAJAN, FORMER SCIENTIST-IN-CHARGE	CENTRAL SCIENTIFIC INSTRUMENTS ORGANISATION, MADRAS CENTRE, CSIR MADRAS COMPLEX, TARAMANI, MADRAS.

PCT International Classification Number

G01N 27/26

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA