METHOD FOR EXTRACTING IODINE FROM AN AQUEOUS SOLUTION

Abstract

The present invention relates to a method for extracting iodine from an aqueous solution, the method comprising the steps: Providing an aqueous solution containing iodide ions; Heating the aqueous solution containing iodide ions; Adding an acid to the aqueous solution to arrive at a pH from 1.5 to 2.5; Adding an oxidizing agent to the aqueous solution to arrive at a E.sub.h from 570 to 590 mV; Desorbing iodine by means of an airflow.

Claims

1. Method for extracting iodine from an aqueous solution, the method comprising the steps: Providing an aqueous solution containing iodide ions; Heating the aqueous solution containing iodide ions; Adding an acid to the aqueous solution to arrive at a pH from 1.5 to 2.5; Adding an oxidizing agent to the aqueous solution to arrive at a E.sub.h from 570 to 590 mV; and Desorbing iodine by means of an airflow.

2. Method according to claim 1 further comprising, after the step of desorbing, one or more of the steps: Adding a sorbent for chemisorbing the iodine; Crystallizing the iodine; Purifying the iodine under a layer of sulfuric acid; Sublimation of the iodine.

3. Method according to claim 1, wherein the aqueous solution containing iodide ions formation and associated waters from oil and gas fields.

4. Method according to claim 1, wherein the aqueous solution containing iodide-ions comprises the iodide ions in an amount of at least 20 mg/l with respect to the total aqueous solution.

5. Method according to claim 1, wherein heating the aqueous solution containing iodide ions comprises heating to a temperature from 30 to 70 C.

6. Method according to claim 1, wherein after adding the acid to the aqueous solution the pH is from 2.0 to 2.5.

7. Method according to claim 1, wherein the acid is sulfuric acid and/or hydrochloric acid.

8. Method according to claim 1, wherein the E.sub.h after adding the oxidizing agent is from 575 to 585 mV.

9. Method according to claim 1, wherein the oxidizing agent is chorine or chlorine water.

10. Method according to claim 1, wherein adding the oxidizing agent to the aqueous solution is carried out under stirring.

11. Method according to claim 1, wherein in the step of adding the oxidizing agent, air is supplied to the aqueous solution.

12. Method according to claim 1, wherein the desorbing is carried out in a vertical column apparatus filled with a desorber packing.

13. Method according to claim 2, wherein the sorbent added for chemisorbing the iodine is sodium hydroxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] FIG. 1 shows a laboratory setup for the study of kinetics of iodine oxidation in aqueous solutions.

[0076] FIG. 2 shows a reactor system for iodine oxidation in aqueous solutions on an industrial scale.

DETAILED DESCRIPTION OF THE INVENTION

[0077] In the following, the present application will be described in detail with reference to the figure. It shall, however, be understood that not all of the preferred features mentioned in the following are necessarily needed for building an inventive device. Rather, one or more of the following preferred features may, separately or in combination, be used, in particular in combination with the above general disclosure of the invention, to realize the inventive method.

[0078] FIG. 1 shows a laboratory setup for the study of kinetics of iodine oxidation in aqueous solutions.

[0079] FIG. 2 shows a reactor system for iodine oxidation in aqueous solutions on an industrial scale.

[0080] The constituents of the laboratory setup shown in FIG. 1 are as follows: [0081] 1. reactor; 2. compressor; 3. sulfuric acid tank; 4. chlorine water tank; 5. drexel (vessel with absorber); 6. gas meter; 7. Electric engine with stirrer; 10. rotameter; 22. electronic temperature controller with thermal resistor.

[0082] Depending on the objective, research on the study of iodine oxidation kinetics by chlorine was conducted in three stages: [0083] 1. Study of iodine oxidation kinetics using chlorine at the temperature of the drilling water of 40 C., 45 C., 50 C.; pH=1.5; 2.0; 2.55; eH=540 to 560 mV; 575 to 585 mV; [0084] 595-615 mV without stirring or air supply. [0085] 2. At the same values of t C. of drilling water, pH, E.sub.h of the solutionwith stirring (at 200 rpm.). [0086] 3. At the same values of t C. of drilling water, pH, E.sub.h of the solutionwith stirring (at 200 rpm) and iodine regeneration through air in the amount of 1.6 m/hour.

[0087] Experiments on the study of iodine oxidation kinetics in drilling water have shown that the process is significantly influenced by: pH of the environment, water temperature, the degree of oxidation (E.sub.h), stirring and air supply.

[0088] The iodine oxidation process in drilling water has its own peculiarities. In salt-free solutions the change in temperature from 20 to 50 C. does not affect the degree of iodine oxidation while in the drilling water at the same degree of oxidation and pH of the environment the rate of iodine transfer from I.sub.2 to I.sup. increases with the temperature increase from 45 C. to 50 C.

[0089] The acidity of the solution influences the kinetics of iodine oxidation as well. With the increase in acidity of the solution there was a decrease in the transfer rate of I.sub.2 to I.sup.. Comparison of the kinetic curves produced at pH 1.5 to 2.0 showed insignificant differences in the [transfer] rate and therefore in order to reduce the consumption of sulfuric acid used for acidification of the solution, the value of water acidity pH=2.0 to 2.5 should be considered optimal.

[0090] The studies on the influence of the amounts of oxidizer (chlorine) consumption in the process of iodine oxidation have shown that in the absence of an oxidizer (E.sub.h=545 to 550 mV.) two forms of iodine (I.sub.2 and I.sup.) are formed in the solution, and after that, in result of the reaction, there is a sharp decrease in I.sub.2 due to its transition to I.sup.. As for the kinetic curves obtained at normal consumption of the oxidizer (E.sub.h=575 to 585 mV.) it has been shown that at E.sub.h=575 mV only I.sub.2 is formed in the solution, that is, there is 100% [pure] I.sub.2. Insignificant oversupply of chlorine water E.sub.h=575 to 585 mV leads to the formation of I.sub.2 and IO.sup.3 at the percentage ratio of I.sub.2=97 to 85% and IO.sup.3=3 to 15%.

[0091] The IO.sup.3 solution is then reduced to I.sub.2 in 5-7 minutes, after which it is transitioned from I.sub.2 to I.sup..

[0092] In case of significant overexposure of the oxidizer (E.sub.h=595 to 615 mV), the process is similar to the previous one but the high amount of IO.sup.3 of 32 to 35% formed in the process is transitioned completely to I.sub.2 in time exceeding 30 minutes.

[0093] Studies to research the effect of stirring on the process of iodine oxidation have shown that the reducing IO.sup.3 to I.sub.2 occurs much faster in 2 to 3 minutes, and the formed IO.sup.3 has enough time to transition in its entirety to I.sub.2 and then to I.sup. in 30 minutes.

[0094] The study of the kinetic curves obtained by stirring the solution and regenerating I.sub.2 from the solution showed that the removal of I.sub.2 from the solution significantly accelerates the process of reduction of IO.sup.3 to I.sub.2 and its subsequent transition to I.sup.. The duration of the reduction process of IO.sup.3 to I.sub.2 and the transition of I.sub.2 to I.sup. takes from 13 to 15 minutes, meanwhile the same process takes more than 60 min in the homogeneous reactor. Thus, it can be assumed that the optimal value of Cl.sub.2/2 I.sup. (provided that the amount of complex ions not involved in the interphase distribution is less than 10%): Cl.sub.2=10%; I.sub.2Cl.sup.=55% and I.sup.=30%. At the given composition I.sup. will influence the shift of equilibrium reaction ICl.sub.2+I.sup.I.sub.2Cl.sup.+Cl.sup. towards the formation of I.sub.2Cl.sup., which easily dissociates to I.sub.2 and Cl.sup..

[0095] On the basis of the received results it is considered expedient to carry out a step-by-step iodine ion oxidation that will necessitate structural changes in hardware setup of the desorber and maintaining of an exact dosage of chlorine in 3 points at the height of the packing. The results of studies on the hydrodynamics of the desorption process at semi-industrial and industrial plants have shown that the period of the liquid phase in the columns depends on the type of packing and hydrodynamic mode of operation of the column and ranges from 0.6 to 5 minutes. When the column operates in the emulsified mode or a similar one with a high-performance partially flooded packing, the time of the liquid phase in the column is 4-5 minutes. In this regard, the use of a highly effective iodine chemodesorption packing will bring the degree of iodine extraction at the stage of air desorption from 95 to 97%.

[0096] This [process] proposal follows from the fact that when chlorine is supplied to the solution in the amount corresponding to the value of pH=575 to 585 mV, from 3 to 15% of iodine is formed in the form of IO.sup.3, which transitions to I.sub.2 in 2 to 5 minutes. In this case, I.sub.2 recovered from IO.sup.3 will be regenerated by the air flow into the gaseous phase and by the time the entire IO.sup.3 is transitioned to I.sub.2 (at the bottom of the column) the remainder of I.sub.2 will also be desorbed into the gas phase. This process does not require any changes in the design of the desorption unit and the introduction of an oxidizer at 3 points at the height of the packing, unlike step-by-step oxidation process. The data obtained from the laboratory setup shows that [the process of] iodine regeneration from the drilling water depends largely on pH, E.sub.h and water temperature. The largest amount of desorbed iodine from drilling water was observed at pH=1.5 and E.sub.h=585 to 605 mV.

[0097] This may be attributed the fact that the presence of iodine in the solution in large amounts of peroxidized IO.sup.3 slows down the transition of I.sub.2 to I.sup. until the entire IO.sup.3 is reduced to I.sub.2, which requires a significant amount of time. The amount of desorbed iodine in the gaseous phase would be much higher than it was recorded in the course of studies if the amount of air supplied to the process was more than 1.6 m.sup.3, which, in our opinion, is an insufficient amount.

[0098] The following conclusions can be made based on the results of the research: [0099] 1. The reaction of iodide oxidation in drilling water differs significantly from the reaction of iodide oxidation in non-saline solutions. [0100] 2. Iodide oxidation depends to a great extent on pH, E.sub.h, temperature of drilling water and stirring; [0101] 3. It is established that the optimal parameters of the solution for iodide oxidation are: pH=2.0-2.5; E.sub.h=575 to 585 mV; [0102] 4. It has been found that the higher degree of iodine desorption from drilling waters necessitates the previous stage of iodine oxidation; [0103] 5. For the purpose of full extraction of iodine from drilling and formation waters of oil and gas fields it is necessary to maintain the degree of iodine oxidation at a level that allowsat the moment when the oxidized drilling water enters the desorberto have 3 to 7% of overoxidized iodine in the solution in the form of IO.sup.3. [0104] 6. Optimal management of the iodine oxidation process depends in each case on the chemical composition of water, water temperature, type of packing and hydrodynamic mode of desorption. [0105] 7. It is found that the performance of the iodine oxidation process at an optimal level is possible through the introduction of a node enabling approximate and precise dosage of chlorine or chlorine-enriched water.

[0106] In the reactor system shown in FIG. 2 initial iodine-containing formation water (aqueous solution) is fed into separators of oil and water 1, where, after the separation of oil and solid impurities, it is supplied to the inlet of a water heater 2, where the aqueous solution is heated to a temperature of 45 to 50 C. and is pumped into a raw water tank 3.

[0107] Then the aqueous solution flows through a 1.5 m diameter fiberglass pipesludge collector 9 to a pump inlet 4 and afterwards to the top of a desorber 5 for irrigation of the desorber packing. Before the aqueous solution enters the desorber, the following parts are added to it: iodine stock solution from a tank 6, concentrated sulfuric acid for achieving a pH from 2.0 to 2.5, concentrated sulfuric acid, and chlorine water from an electrolyzer 8 for iodine oxidation.

[0108] Acidified and oxidized oil formation water containing iodine ions goes to the top of the desorber 5 and is evenly distributed over the active section of the column using irrigators. Flows of acidified and oxidized iodine-containing oil water flow down packings 10 and 11 while spreading into individual thin streams. An airflow is blown forming a counterflow from bottom to the top using a fan 12 with a speed of 1.7-1.85 m/sec against the water streams containing elementary iodine. In the course of this process takes place the desorption (transition) by air of elementary iodine from oil water into gaseous phase through the packing layer. The desorber 5 is a vertical cylindrical device made of titanium with an internal diameter of 2.0 to 3.4 m and a height of 12 to 15 m filled up to on two levels with heights 2 and 5 meters respectively with a highly effective packing.

[0109] The efficiency of the iodine desorption process depends on the specific surface of the packing used in the desorber, the temperature of the drilling water and the amount of air supplied for iodine blowing. Acidified and oxidized iodine-containing formation water is depleted from iodine as it flows down the packing, and the air supplied from the bottom to the top of the desorption column is enriched with iodine vapor as it rises to the top of the desorption column.

[0110] After iodine extraction, the spent acidified formation water is removed from the lower part of the desorption column through a hydrosealing device that prevents the air from escaping, and then goes to a unit 13 for its neutralization by alkaline solution from the electrolyzer 8 and by lime milk (calcium oxideCaO) supplied to the neutralizing unit 13 until it reaches the value of pH=7.0 to 7.5. Afterwards, the treated and neutralized formation water is sent back to the plant for utilization of formation oil waters with further pumping of these waters into the absorbing horizons of oil wells.

[0111] The iodine/air mixture from the top of the desorber 5 flows through a duct 14 to the bottom of the absorber 15 and spreads in the process of its passing through the grate and packing 16, then it is directed to the upper part of the absorption column 15. Against the iodine-air mixturefrom top to the bottomadsorbent flows down (sodium-hydroxide solution) from the sorbent circulation tank 17, by means of a centrifugal pump 18 to the absorption column irrigator. Chemisorption processes take place on the surface of the packing between iodine and sodium hydroxide solutions. The design of the absorber is similar to that of the desorber and differs only in the height of the column9 to 10 m and the height of the packing (5 m). As the sorbent flows down, the sorbent is enriched with iodine and iodate (the total iodine content), and the iodine gets extracted from the air as it rises up the column. After iodine has been extracted (captured) from it, the air escapes to the atmosphere through an exhaust pipe 19.

[0112] The sorbent solution is continuously circulating as per the following scheme:

K-15->E-17->K-15->E-17

[0113] As the iodine sorbent circulates, it is continuously enriched with iodine, i.e. the concentration of iodide I.sup. and iodate IO.sub.3 ions increases, and the content of sodium hydroxide accordingly decreases.

[0114] Lack of sodium hydroxide is compensated by the addition of a sorbent. For normal operation, the pH of the sorbent should be maintained within 9 to 11. After reaching the concentration of general iodine to 80-120 g/l, the basic part of a sorbent is gradually removed to the crystallizer 19 where the fresh water is continuously supplied from the tank for the purposes of cooling and rinsing.

[0115] When concentrated sulphuric acid and chlorine are continuously added from the tank 19, iodine paste gets extracted, which is fed to the Nutch Filter 20 and then sent to the iodine melting node under the layer of sulphuric acid 21 or to the iodine sublimator 22 and then for its package 23.

[0116] In order to reduce sulphuric acid consumption, the spent stock solution after the Nutch Filter 20 is fed to the stock solution receiving tank 6 and then added through the pipeline to iodine-containing water supply to the desorber 5. The iodine paste obtained through the filter is rinsed with the fresh water in the volume equal to the weight of the rinsed iodine (1 kg-1 liter of water) and then dried by suction of air through the iodine paste layer with a vacuum pump.

[0117] The refining device (iodine melter) 21 operates at a the temperature of 120 to 140 C. The temperature is maintained using four 1.5 kW heaters. Temperature control is maintained automatically using contact thermometers. Concentrated sulfuric acid and iodine paste are supplied from above. The acid is supplied from the pressure tank 7 with the force of gravity and the iodine paste is loaded manually.

[0118] Refined iodine is removed from the bottom of the unit through the packing, preventing the ingress of sulfuric acid into the finished product. Waste acid is removed from the side outlet and then used to acidify the initial water. Refined iodine is collected in the finished product collector units made of PTFE.

[0119] Iodine extracted to the collector units is then crushed and packaged per 50 kg into the drums with inserts made of polyethylene terephthalate film. The iodine is then fed into the unit 22 for the purpose of obtaining sublimated iodine and, after drying, is then fed to the packaging machines 23. The sublimated or technical iodine obtained shall conform the international standards in terms of its composition and package and shall be distributed in the following packages: 50 kg, 10 kg, 3 kg, 0.5 kg.

[0120] This technology of iodine production is modern, low-waste and ecologically safe. Waste acidic water from desorber is discharged to a reactor with a stirring device 13, into which the lime milk and alkali from the electrolyzer 8 are fed. Discharge water, after its neutralization with lime milk and alkali to pH 7.0 goes into waste water collector 26 and is then pumped into the waste oil formation water reservoirs.

[0121] In order to prevent harmful emissions of iodine vapor formed at the stages of crystallization, purification (sublimation) and scaling from escaping into the atmosphere, those emissions are driven by a fan 24 to the scrubbing packing 25 where the emissions are captured by a liquid absorber pumped 28 from the tank 27. The yield of the finished product (iodine of AR or LR) using this technology is 85 to 88%.

[0122] The features disclosed in the foregoing description, in the claims and the accompanying drawings may, both separately or in any combination, be material for realizing the invention in diverse forms thereof.