Process for obtaining iodide from solutions comprising iodine-containing aromatic compound

Abstract

The invention refers to a process for obtaining iodide from solution comprising low amounts of iodine-containing aromatic compound, such as of non-ionic X-ray contrast agents, comprising the steps of contacting the solution comprising low amounts of iodine-containing aromatic compound with activated carbon to adsorb the iodine-containing aromatic compound comprised therein onto the activated carbon; and de-iodinating the iodine-containing aromatic compounds adsorbed onto the activated carbon.

Description

[0001] PROCESS FOR OBTAINING IODIDE FROM SOLUTIONS COMPRISING IODINE- CONTAINING AROMATIC COMPOUND

[0002] Technical field

[0003] The invention relates to a process for recovering iodide from solutions comprising low amounts of iodine-containing aromatic compounds.

[0004] Background art

[0005] Iodine-containing aromatic compounds find several uses in different technical fields, such as in the diagnostic field. Indeed, radiographic contrast agents commonly used in clinical applications, namely non-ionic X-ray contrast agents, are iodine-containing aromatic compounds. The structure of commonly used non-ionic X-ray contrast agents is indeed characterized by three-iodinated aromatic ring(s), wherein iodine is covalently bonded to a carbon atom of the aromatic ring(s). Examples of non-ionic X-ray contrast agents are iodixanol, iohexol, iopentol, iopromide, ioversol, ioxilan, iosarcol, iogulamide, iodamide, iomeprol, iobitridol, and iopamidol.

[0006] Iodine recovery is a key part in the manufacture of iodine-containing aromatic compounds, both for economic and for environmental reasons. Indeed, iodine is an expensive and rare starting material, and its discharge is subject to very strict limitations. Iodine is conventionally recovered by de-iodinating iodine-containing aromatic compounds, so that the covalent bond between iodine and carbon is cleaved, thereby obtaining iodide (typically dissolved within an aqueous solution). Iodide can then be converted according to known processes e.g. to any specific form conventionally used for iodination and / or to molecular iodine (I2). Thus, obtaining iodide is a key point for iodine recovery.

[0007] During the manufacture of iodine-containing aromatic compounds, residual amounts of the same can be lost due to plant losses, leaks, industrial washings, and other similar operations. In view of the economic and environmental reasons mentioned above, iodine recovery even from these residual amounts is important. However, it can be difficult to recover iodine with satisfactory yields from wastewaters comprising residual amounts of iodine-containing aromatic compounds, especially from tri-iodo aromatic compounds having highly substituted pendant moieties, such as from non-ionic X-ray contrast agents for clinical use.

[0008] WO 2018 / 224581 discloses a process for the recovery and recycling of iodine from aqueous solutions comprising iodine-containing aromatic compounds at pH lower than 1 in the absence of a catalyst. This document further discloses a step for recovering optional residual traces of organic iodine, such step comprising (i) feeding the aqueous liquors deriving from the upstream steps into columns loaded with carbon, whereby organic iodine fixes onto the carbon, and then (ii) desorbing the fixed organic iodine using suitable solvents or bases (such as 30% NaOH, in the absence of a catalyst), thus providing a concentrated solution of organic iodine that can be conventionally treated to obtain iodide. WO 2018 / 224581 exemplifies the treatment of mono-, di-, and tri-iodinated derivatives of 5-amino-l,3- benzendicarboxylic acid according to this absorbing-desorbing procedure:

[0009] Tri-iodinated derivative of 5-amino-l,3-benzendicarboxylic acid

[0010] These derivatives are common intermediates of some iodine-containing aromatic compounds conventionally used in clinical applications for X-ray imaging, e.g. iopamidol, and bond simpler and lighter pendant groups compared to the latter.

[0011] In view of the above, there is the need to provide processes for treating wastewaters comprising low amounts of iodine-containing aromatic compounds with satisfactory yields, such processes not being necessarily limited to treating common intermediates of non-ionic X-ray contrast agents; that is, there is the need to provide processes for treating also iodine- containing aromatic compounds bonding more elaborate and heavier pendant groups compared to the ones mentioned in the prior art, e.g. for treating wastewaters containing non-ionic X-ray contrast agents for clinical use.

[0012] Summary of the invention

[0013] The invention relates to a process for obtaining iodide as set out in claim 1.

[0014] As mentioned above, obtaining iodide is a key step for the recovery of iodine from solutions comprising iodine-containing aromatic compounds.

[0015] The process of the invention advantageously allows obtaining iodide (which, in turn, allows recovering iodine) from solutions comprising low amounts (such as the amounts mentioned below) of iodine-containing aromatic compounds in a manner that is environmentally friendly and that provides good yields.

[0016] In particular, it has been found that treating solutions comprising low amounts (e.g. the amounts mentioned below) of iodine-containing aromatic compounds can be effectively carried out by first adsorbing the iodine-containing aromatic compounds onto activated carbon (preferably using the conditions as set out in any one of the embodiments herein disclosed), and then by de-iodinating such adsorbed iodine-containing aromatic compounds directly while they are adsorbed onto the activated carbon, thus obtaining iodide. By operating as such, after de-iodination, the activated carbon can be regenerated; indeed, it has been found that it is easier to desorb the species adsorbed therein when they have been de-iodinated. This improves the environmental impact of the process, in that activated carbon does not need to be discharged after carrying out the process of the invention, and indeed can be used again after its regeneration.

[0017] Thus, differently from the prior art process, the process of the invention does not provide for desorbing the iodine-containing aromatic compounds before their de-iodination. Instead, the process of the invention provides for carrying out the de-iodination step b) while the iodine-containing aromatic compounds are still adsorbed onto the activated carbon.

[0018] Moreover, differently from the prior art process, the process of the invention can advantageously be used also for solutions comprising low amounts (e.g. the amounts mentioned below) of non-ionic X-ray contrast agents, in particular the ones for clinical use. Indeed, it has been found that carrying out the prior art process for obtaining iodide on solutions comprising low amounts of a non-ionic X-ray contrast agents for clinical use, e.g. iopamidol, is far from efficient, particularly due to the desorption step. This is demonstrated in the experimental section below (see Example 1 (Comparative)), wherein desorption from adsorbents like activated carbon of an iodine-containing compound bonding more elaborate and heavier pendant groups compared to mono-, di-, and tri-iodinated derivatives of 5-amino- 1,3-benzendicarboxylic acid (as provided for in the prior art) has proven to be unsatisfactory. Accordingly, the process of the invention advantageously dispenses of the desorption step, which requires high amounts of e.g. solvents or bases to effectively desorb iodine-containing aromatic compounds. Not carrying out the desorption step further allows to save time.

[0019] The process of the invention allows obtaining an amount of iodide that is 70% or more, preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, and most preferably 99% or more of the total amount of adsorbed organic iodine. Considering that the process of the invention allows treating highly diluted solutions ( / .e. solutions comprising the amounts mentioned below of iodine-containing aromatic compound), which cannot be effectively treated according to the prior art process (in particular, when the iodine- containing aromatic compound is a non-ionic X-ray contrast agent for clinical use - see Example 1 (Comparative)), these yields can be considered very good.

[0020] Embodiments of the present invention are set out in the dependent claims and in the detailed description of the invention.

[0021] Detailed description of the invention

[0022] A first aspect of the invention is a process for obtaining iodide (I ) from an aqueous solution comprising at least an iodine-containing aromatic compound, the iodine-containing aromatic compound being in an amount of 2% w / w or lower within the aqueous solution, the process comprising the following steps: a) contacting the aqueous solution with activated carbon to adsorb the iodine- containing aromatic compound comprised therein onto the activated carbon; and b) de-iodinating the iodine-containing aromatic compounds adsorbed onto the activated carbon, preferably by contacting the iodine-containing aromatic compound adsorbed onto the activated carbon with copper ions and OH- ions, preferably at a temperature higher than 100 °C, thus obtaining iodide. OH- can be in an amount of 0.5 moles per moles of adsorbed organic iodine or higher, e.g. 0.5 moles to 30 moles per moles of adsorbed organic iodine. Copper ions are preferably Cu2+ions.

[0023] As used herein, the term "iodine-containing aromatic compound" refers to any compound comprising within its structure (i) a (hetero)aromatic ring, preferably an aromatic ring, and (ii) at least an iodine atom (such as three to six iodine atoms) covalently bonded to a respective carbon atom, preferably a carbon atom of the (hetero)aromatic ring; such iodine atom is herein identified as "organic iodine". Suitable and preferred examples of iodine- containing aromatic compounds are non-ionic X-ray contrast agent, preferably commercial products for clinical use. Preferred non-ionic X-ray contrast agents are set out in the embodiments below. Each of the non-ionic X-ray contrast agent mentioned below comprises three organic iodine as previously defined, except for iodixanol, which comprises six organic iodine.

[0024] As used herein, the term "activated carbon" refers to a material suitable for adsorbing molecules, such as iodine-containing aromatic compound as previously defined. The composition of activated carbon can vary and depends on the materials from which it derives. Activated carbon is also commonly known as active carbon, activated charcoal, or active charcoal. Preferred types of activated carbon are set out in the embodiments below.

[0025] According to a preferred embodiment, the iodine-containing aromatic compound is a non-ionic X-ray contrast agent, such as a non-ionic X-ray contrast agent selected from the group consisting of iodixanol, iohexol, iomeprol, iopamidol, iopentol, iopromide, ioversol, ioxilan, iosarcol, iogulamide, iobitridol, and iodamide. According to a more preferred embodiment, the non-ionic X-ray contrast agent is for clinical use, and is selected from the group consisting of iopamidol, iomeprol, iohexol, ioxilan, iopromide, iobitridol, iodixanol, iobitridol and ioversol; even more preferably of iomeprol and iopamidol; and most preferably is iopamidol. Indeed, it has been surprisingly found that obtaining iodide (and thus, recovering iodine) from diluted solutions of non-ionic X-ray contrast agents (particularly for the ones for clinical use), such as from solutions comprising low amounts of iodine-containing aromatic compounds set out above, cannot effectively be done according to the prior art process, that is by first adsorbing and then desorbing the non-ionic X-ray contrast agent to be treated; this is demonstrated in Example 1 (Comparative). Since the process of the invention can be effectively used to obtain iodide from solutions of i.a. non-ionic X-ray contrast agents, for example for clinical use, the process of the invention can be effectively used as well to obtain iodide from solutions of iodine-containing aromatic compounds bonding lighter pendant groups than non-ionic X-ray contrast agents for clinical use, the former being for example intermediates of non-ionic X-ray contrast agents for clinical use, e.g. mono-, di-, or tri-iodinated derivative of 5-amino-l,3-benzendicarboxylic acid.

[0026] As mentioned above, the process of the invention allows obtaining iodide (and thus, allows recovering iodine) from a solution comprising low amounts of iodine-containing aromatic compounds, such as of 2% w / w or lower. According to a preferred embodiment, the amount of iodine-containing aromatic compound, preferably of non-ionic X-ray contrast agent (e.g. for clinical use), such as the list of non-ionic X-ray contrast agents mentioned above, is of 1.0% or lower, preferably of 0.5% w / w or lower, more preferably of 0.05% w / w or lower, even more preferably of 0.02% w / w or lower, such as for example 0.01% w / w or lower, down to e.g. 0.001% w / w.

[0027] According to step a) of the process of the invention, the aqueous solution comprising the iodine-containing aromatic compound, such as the non-ionic X-ray contrast agent, e.g. the ones mentioned above, is contacted with activated carbon, whereby the iodine-containing aromatic compound is adsorbed onto the activated carbon. This step can be carried out for example by flowing the aqueous solution through activated carbon, which can be conveniently arranged and packed within one or more columns, such as two or more columns, in parallel and / or in series.

[0028] According to an embodiment, the activated carbon is granular activated carbon, which has been found to be in a more suitable form (that is, granular) to adsorb the iodine- containing aromatic compound according to step a) of the process of the invention compared to standard activated carbon. Moreover, granular activated carbon can advantageously be packed within one or more columns. According to an embodiment, 10 wt% or less of the granular activated carbon have a particle size lower than 0.425 mm (40 mesh), and 15 wt% or less of the granular activated carbon have a particle size higher than 1.70 mm (12 mesh). Preferably 5 wt% or less, more preferably 4 wt% or less, of the particle size is lower than 0.425 mm (40 mesh); preferably 10 wt% or less, more preferably 5 wt% or less, of the particle size is higher than 1.70 mm (12 mesh).

[0029] According to an embodiment, the (granular) activated carbon is able to withstand temperatures of at least 100 °C, such as of at least 120 °C or 145 °C, meaning that it does not substantially degrade from a mechanical standpoint. It has been found that (granular) activated carbon made of coal, such as bituminous coal, can withstand such temperatures, whereby this type of (granular) activated carbon is preferred; (granular) activated carbon made of at least 50% coal, preferably of at least 70% coal, more preferably of at least 80% coal, and even more preferably of 90% coal, are particularly preferred. Particularly preferred is granular activated carbon obtained by bituminous coal that is steam activated, pulverized, and finally agglomerated into granular form.

[0030] As mentioned above, step a) can be carried out by flowing the aqueous solution comprising the iodine-containing aromatic compound through the (granular) activated carbon, which can be conveniently arranged in one or more columns. Accordingly, after step a), e.g. downstream of the column(s) of (granular) activated carbon, the aqueous solution contains lower amount of iodine-containing aromatic compounds compared to before step a) (e.g. upstream of the column(s) of (granular) activated carbon), such as substantially no iodine-containing aromatic compounds (meaning that the yield of adsorption can be substantially quantitative), at least until the (granular) activated carbon is still able to effectively adsorb all the iodine-containing aromatic compound contacting it (based on several factors, e.g. the flow rate of the aqueous solution, the concentration of the iodine-containing aromatic compound within the aqueous solution, etc. , or at least until the (granular) activated carbon is saturated with the iodine-containing aromatic compound. Thus, after step a), the aqueous solution comprising possibly substantially no iodine-containing aromatic compound can be conveniently flowed to conventional wastewater treatment plants. This embodiment is advantageous, particularly when the activated carbon is arranged within two columns or more, because the process can be carried out in continuous; indeed, according to such embodiment, step b) can be carried out within the column comprising the saturated activated carbon, or comprising the activated carbon that cannot effectively adsorb all the iodine-containing aromatic compound, while the activated carbon comprised in the other column(s) can effectively adsorb the iodine-containing aromatic compounds contacting it (step a)), thus avoiding or reducing possible losses of iodine-containing aromatic compound.

[0031] According to a preferred embodiment, when step a) is carried out by flowing the aqueous solution comprising the iodine-containing aromatic compound through the (granular) activated carbon, the flow rate of the aqueous solution is such that the aqueous solution, after being flowed through the (granular) activated carbon, does not substantially contain iodine- containing aromatic compound; this can be monitored via conventional means, e.g. via UV spectrometry, by setting the wavelength of the detector to detect the relevant iodine- containing aromatic compound (such as 280 nm for iopamidol). According to this preferred embodiment, the flow rate can thus depend on several factors, e.g. on the amount and type of (granular) activated carbon, and on the concentration and type of iodine-containing aromatic compound.

[0032] The amount of time to carry out step a) can vary. Indeed, step a) can be carried out for an amount of time sufficient for the (granular) activated carbon to be saturated with the iodine-containing aromatic compound, such as with the non-ionic X-ray contrast agent e.g. mentioned above. When step a) is carried out by flowing the aqueous solution comprising the iodine-containing aromatic compound in the amounts mentioned above through the (granular) activated carbon, the saturation of the (granular) activated carbon is reached when the amount of iodine-containing aromatic compound within the aqueous solution downstream of the (granular) activated carbon is the same as the amount of iodine-containing aromatic compound within the aqueous solution upstream of the (granular) activated carbon. This amount of time can thus depend on e.g. the amount and type of iodine-containing aromatic compound, the amount and type of (granular) activated carbon, and on the flow rate of the aqueous solution.

[0033] Step b) of the process of the invention can be carried out according to known methods for de-iodinating; for example, step b) can be carried out contacting copper ions, preferably Cu2+ions, and OH- ions, preferably both comprised within an aqueous solution, directly with the iodine-containing aromatic compounds adsorbed onto the activated carbon. Copper ions, such as Cu2+ions, and OH-, e.g. when comprised within an (aqueous) solution, are able to de-iodinate iodine-containing aromatic compounds, in particular when the contacting occurs and is maintained at a temperature of 100 °C or higher, as known from e.g. EP0106934. Thus, differently from the prior art process, the process of the invention does not provide for a desorption step between step a) and step b), that is a step carried out to purposefully desorb the iodine-containing aromatic compounds from the (granular) activated carbon before de-iodination, and thus before the obtainment of iodide. It has been found that, after step b), the compounds that have been de-iodinated are desorbed more easily compared to before their de-iodination. Accordingly, after de-iodination, the activated carbon can be regenerated by desorbing the compounds that have been de-iodinated, advantageously avoiding the need to dispose of the activated carbon; indeed, according to an embodiment, after the de- iodination step b), the activated carbon is used again for step a).

[0034] The output of step b) is the cleavage of at least some, such as most, if not all, of the covalent bonds between iodine and carbon atoms; indeed, the yield of the process of the invention is at least 70%, preferably at least 80%, more preferably at least 90%, even more preferably 95% or more, and most preferably 99% or more, considering the amount of adsorbed organic iodine vs. the amount of recovered iodide. Step b) provides iodide within a solution, i.e. advantageously not adsorbed onto the activated carbon; thus, the solution comprising the obtained iodide can be flowed to conventional plants allowing the conversion of iodide into any iodinating species and / or into molecular iodine (h) through conventional means.

[0035] According to an embodiment, the amount of OH- ions to be contacted with the iodine- containing aromatic compound adsorbed onto the (granular) activated carbon is 0.5 moles or higher, such as 1 mole or higher; according to an embodiment, the amount is 0.5 to 30 moles, preferably 1 to 15 moles, more preferably 1.5 to 10 moles, and even more preferably 2 to 6 moles, such as 2.5 to 5.4 moles, per moles of adsorbed organic iodine.

[0036] As used herein, "adsorbed organic iodine" refers to the amount of organic iodine as previously defined that is adsorbed onto the (granular) activated carbon after carrying out step a). The amount of adsorbed organic iodine can be determined according to conventional methods, e.g. it can be calculated based on the amount and type of (granular) activated carbon used for the process of the invention, and / or based on the amount and type of iodine- containing aromatic compounds comprised within the aqueous solution contacted with the (granular) activated carbon.

[0037] According to an embodiment, the amount of copper ions, preferably of Cu2+ions, to be contacted with the iodine-containing aromatic compounds adsorbed onto the (granular) activated carbon is catalytic, and can be of at least 0.0001 moles, preferably at least 0.0002 moles, more preferably at least 0.0003 moles, most preferably at least 0.0004 moles, such as 0.0008 moles, per moles of adsorbed organic iodine; the amount can be e.g. as high as 0.01 moles per moles of adsorbed organic iodine. This embodiment is particularly advantageous both industrially and environmentally; indeed, compared to the amount of iodine-containing aromatic compound, copper ions can be used in very small amounts (catalytically) in order to de-iodinate the iodine-containing aromatic compound.

[0038] According to an embodiment, copper ions (such as Cu2+) and / or OH- can be contacted in the amounts mentioned above with the iodine-containing aromatic compounds adsorbed onto the (granular) activated carbon by means of a solution, preferably an aqueous solution, comprising copper ions and / or OH-. The (aqueous) solution comprising copper ions (such as Cu2+) and / or OH- can be advantageously prepared by adding to the (aqueous) solution a salt forming copper ions (preferably forming Cu2+) and / or OH- when dissolved, such as CuSCU and / or NaOH. The (aqueous) solution comprising the amounts mentioned above of copper ions and / or OH- can then be contacted with the iodine-containing aromatic compounds adsorbed onto the (granular) activated carbon, thereby in turn contacting the latter with copper ions and / or OH-.

[0039] According to an embodiment, step b) is carried out at a temperature of 100 °C or higher, preferably of 110 °C or higher, and more preferably of 120 °C or higher, and can be as high as e.g. 180 °C. Carrying out step b) at such temperatures promotes de-iodinating the iodine- containing aromatic compounds.

[0040] The amount to carry out step b) can vary, and can depend on e.g. the temperature at which step b) is carried out. According to an embodiment, step b) is carried out for a time of 1 hour or more, preferably of 3 hours or more, more preferably of 5 hours or more, even more preferably of 10 hours or more, and most preferably for 20 hours or more, such as for 40 hours or more. The time to carry out step b) can be determined on a case-by-case basis e.g. based on the amount of obtained iodide; in particular, step b) can be carried out for a time sufficient to reach the expected yield of obtained iodide, that is a yield of at least 70%, preferably of at least 80%, more preferably of at least 85%, even more preferably of at least 90%, and most preferably of at least 95%, such as of at least 99%. Experimental section

[0041] Material and methods

[0042] Reactants and / or solvents employed in the following Examples that are not specifically synthesized are known and readily available. If they are not commercially available per se, they may be prepared according to known methods in literature.

[0043] The amount of iopamidol can be determined via liquid chromatography, such as via HPLC, according to known methods, e.g. by carrying out the chromatography protocol disclosed in the US Pharmacopoeia USP-NF 2023; USP Monographs: Iopamidol.

[0044] The amount of iodide can be determined via potentiometric titration with AgNCU according to known methods.

[0045] Example 1 (Comparative) - Adsorption and desorption of the iodine-containing aromatic compound iopamidol

[0046] 30 g of granular activated carbon (Norit® 12x40) was added to a jacketed glass chromatographic column of 4.2 cm of diameter, and pre-treated to remove small, powdered particles by flowing 5 BV of water (350 mL) at 3 BV / h (bed volume per hour), then by counterflowing 5 BV of water (350 mL) at 3 BV / h, and finally by flowing again 5 BV of water (350 mL) at 3 BV / h. A 2% w / w aqueous solution of iopamidol at a rate of 1 BV / h was flowed through the granular activated carbon column, to adsorb the iodine-containing aromatic compound iopamidol onto the granular activated carbon.

[0047] The desorption step (not according to the invention) to detach the adsorbed iopamidol from the granular activated carbon was carried out by heating the column at 60 °C and by flowing through the column 1 BV of a pre-heated 10% NaOH solution, then 4 BV of pre-heated water, then further 2 BV of a pre-heated 10% NaOH solution; finally, the granular activated carbon column was kept for about 24 hours at 60 °C in a 10% NaOH solution, and was washed by eluting 2 BV of water.

[0048] Fractions of 1 BV were collected during the desorption step and analysed via HPLC to determine the amount of iopamidol desorbed from the granular activated carbon. After the desorption step, the amount of iopamidol collected was 20.4% with respect to the amount of iopamidol adsorbed onto the granular activated column.

[0049] The present comparative example shows that it is not effective to first adsorb and then desorb iodine-containing aromatic compound as provided for by the prior art process, in particular when the iodine-containing aromatic compound is a non-ionic X-ray contrast agent, such as one for clinical use (e.g. iopamidol). Indeed, differently from the compounds tested in the prior art (that is, mono-, di- and tri-iodinated derivatives of 5-amino-l,3- benzendicarboxylic acid), the yield of iopamidol desorption has been found to be merely 20.4%, whereby the maximum yield of iodine obtainable according to the prior art process (when considering the yield of de-iodination step quantitative) would be in turn 20.4%. Example 2 - Adsorption and de-iodination of the iodine-containing aromatic compound iopamidol

[0050] 120 g of fresh granular activated carbon GAC CAL-I 12x40 (Chemviron) (BV of 280 mL) were loaded into a glass column with an internal diameter of 3 cm and a carbon bed height of 50 cm. The carbon was pre-treated by backwashing with about 10 L of water to obtain a homogeneous carbon bed without air; backwashing was stopped when there was no more release of powder and air bubbles stopped. The experimental setup comprised an open system, and the solution comprising the iodine-containing aromatic compound iopamidol was loaded onto the column by using peristaltic pump. At the end of the column, a Knauer UV- detector with a path length of 2 mm was connected to record the absorbance at a wavelength of 280 nm, whereby it could be determined when iopamidol would no longer be retained by the carbon. A 2% w / w iopamidol solution was flowed through the glass column with a flowrate of 3 BV / h so that iopamidol is adsorbed onto the granular activated carbon; then, the granular activated carbon adsorbing iopamidol was recovered from the glass column, and loaded into a high-pressure steel reactor, provided with an electric heating jacket with a temperature controller. Then, the following was loaded into the reactor: water, 30% NaOH w / w, and CUSO4' 5H2O according to the stoichiometric ratio of NaOH / adsorbed organic iodine of 5.4 mol / mol; and Cu2+I adsorbed organic iodine of 0.0004 mol / mol. The obtained suspension was heated at 145 °C for a total time of 4 hours for promoting de-iodination. The suspension was then cooled at room temperature and filtered (with a sintered glass filter, porosity = 3, 0 = 10 cm with filter paper). The liquor was collected into a tared flask and weighted. The carbon was washed on the filter with water (in an amount of 1.2*BV) and the liquor was collected into a different tared flask and weighted. A weighted aliquot of the two collected solutions was acidified with HNO3 10% w / w up to a pH of 2-2.5 and the amount of iodides recovered was determined with a potentiometric titration with 0.1 N AgNOs. Finally, the carbon was weighted and transferred into a glass column (internal diameter of 3 cm). A second washing was carried out into the column by using 1.5*BV of water. This washing was collected into a bottle and weighted, then a weighted aliquot of solution was acidified with HNO3 10 %w / w up to a pH of 2-2.5 and the number of iodides recovered was determined with a potentiometric titration with 0.1 N AgNCh. Total iodides recovery: 97% (considering the amount of adsorbed organic iodine vs. iodides obtained after the de-iodinating step b)).

[0051] Example 3 - Three cycles of adsorption and de-iodination of the iodine-containing aromatic compound iopamidol

[0052] 120 g of granular activated carbon CAL-I 12x40 (BV of 280 mL) were used for 3 cycles of adsorption and de-iodination as described in Example 2. In particular: fresh granular activated carbon was used for the first cycle (comprising adsorption and de-iodination steps as described in Example 2) with a fresh solution comprising 2% of iopamidol. After the end of the de-iodination step of the first cycle, the carbon was loaded again into a glass column and submitted to a further cycle (comprising adsorption and de-iodination steps as described in Example 2) with a fresh solution comprising 2% of iopamidol. After the end of the deiodination step of the further cycle, the carbon was loaded again into a glass column and submitted to a final cycle (comprising adsorption and de-iodination steps as described in Example 2) with a fresh solution comprising 2% of iopamidol. Table 1 shows the yield for each cycle performed (calculated considering the adsorbed organic iodine vs. the recovered iodides for each cycle).

[0053] Table 1

[0054] Example 4 - Adsorption of the iodine-containing aromatic compound iopamidol

[0055] Several adsorption trials using fresh granular activated carbon were carried out as described in Example 2. Table 2 reports the amount of fresh granular activated carbon (dry), the concentrations of the solutions of iopamidol, the flow rate of the solutions, and the percentage of iopamidol adsorbed onto the activated carbon for each trial. The percentage of iopamidol adsorbed onto the activated carbon was determined based on the total amount of iopamidol comprised within the solution before and after its flow through the activated carbon. The granular activated carbon used was Norit® 12x40 for Trials 1, 2 and 4, and Chemviron CAL-I 12x40 for Trial 3.

[0056] Table 2

[0057] Table 2 shows that the activated carbon is able to effectively adsorb iopamidol; in particular, for Trials 3 and 4, iopamidol was completely adsorbed onto the granular activated carbon, whereas Trials 1 and 2 were interrupted when the UV detector detected iopamidol within the aqueous solution downstream to the granular activated carbon, thus providing an adsorption of 87.76% and 81.10%. Accordingly, depending on the conditions of step a), e.g. aqueous solution flow rate, concentration of the iodinate-containing aromatic compound comprised within the aqueous solution, etc., the activated carbon can adsorb the iodinate- containing aromatic compound in an amount higher than 80%, and as high as 100%, even when the iodine-containing aromatic compound (e.g. iopamidol) is in solution at a concentration as low as 0.1%.

[0058] Once the adsorption step is carried out as provided for in this Example, the de-iodinating step can be carried out according to the process of the invention, e.g. as disclosed in Example 2, thereby obtaining iodide in yields of at least about 70%, and even higher than 90%.

[0059] Example 5 - Adsorption and de-iodination of the iodine-containing aromatic compound iopamidol at industrial scale

[0060] 2600 kg of granular activated carbon CAL-I 12x40 were packed into stainless steel AISI 316 columns. A solution of about 0.01% w / w of iopamidol is flowed through the activated carbon, whereby the activated carbon adsorbed iopamidol. The solution is flowed until iopamidol is detected within the solution flowing downstream of the columns (via UV detector at 280 nm). Then, an amount of 5.4 mol / mol of NaOH per adsorbed organic iodine, and of 0.0008 mol / mol of Cu2+per adsorbed organic iodine was added to the column containing the granular activated carbon adsorbing iopamidol. The column was then heated to 120 °C for more than 24 hours. The yield of the present process was about 73% w / w (considering the amount of obtained iodide vs. the amount of adsorbed organic iodine).

[0061] Example 6 - Adsorption and de-iodination of the iodine-containing aromatic compound iopamidol at industrial scale

[0062] 2600 kg of granular activated carbon CAL-I 12x40 were packed into stainless steel AISI 316 columns. A solution of about 0.01% w / w of iopamidol is flowed through the activated carbon, whereby the activated carbon adsorbed iopamidol. The solution is flowed until iopamidol is detected within the solution flowing downstream of the columns (via UV detector at 280 nm). Then, an amount of 5.4 mol / mol of NaOH per adsorbed organic iodine, and of 0.0008 mol / mol of Cu2+per adsorbed organic iodine was added to the column containing the granular activated carbon adsorbing iopamidol. The column was then heated to 120 °C for more than 40 hours. The yield of the present process was about 99% w / w (considering the amount of obtained iodide vs. the amount of adsorbed organic iodine).

Claims

CLAIMS1. A process for obtaining iodide (I ) from an aqueous solution comprising at least an iodine-containing aromatic compound, the iodine-containing aromatic compound being in an amount of 2% w / w or lower within the aqueous solution, the process comprising the following steps: a) contacting the aqueous solution with activated carbon to adsorb the iodine-containing aromatic compound comprised therein onto the activated carbon; and b) de-iodinating the iodine-containing aromatic compound adsorbed onto the activated carbon, thus obtaining iodide.

2. The process according to claim 1, wherein the amount of iodine-containing aromatic compound is of 1.0% or lower.

3. The process according to claim 2, wherein the amount of iodine-containing aromatic compound is of 0.5% w / w or lower.

4. The process according to claim 3, wherein the amount of iodine-containing aromatic compound is of 0.05% w / w or lower.

5. The process according to claim 4, wherein the amount of iodine-containing aromatic compound is of 0.02% w / w or lower.

6. The process according to claim 5, wherein the amount of iodine-containing aromatic compound is of 0.01% w / w or lower.

7. The process according to any one of claims 1 to 6, wherein the iodine- containing aromatic compound is a non-ionic X-ray contrast agent.

8. The process according to claim 7, wherein the non-ionic X-ray contrast agent is selected from the group consisting of iodixanol, iohexol, iomeprol, iopamidol, iopentol, iopromide, ioversol, ioxilan, iosarcol, iogulamide, iobitridol, and iodamide.

9. The process according to claim 8, wherein the non-ionic X-ray contrast agent is selected from the group consisting of iopamidol, iomeprol, iohexol, ioxilan, iopromide, iobitridol, iodixanol, iobitridol and ioversol; more preferably of iomeprol and iopamidol.

10. The process according to claim 9, wherein the non-ionic X-ray contrast agent is iopamidol.

11. The process according to any one of claims 1 to 10, wherein step a) is carried out by flowing the aqueous solution through activated carbon.

12. The process according to claim 11, wherein activated carbon is arranged within one or more columns.

13. The process according to claim 12, wherein activated carbon is arranged within more than one column.

14. The process according to any one of claims 1 to 13, wherein activated carbon is granular activated carbon.

15. The process according to claim 14, wherein 10 wt% or less of the granular activated carbon have a particle size lower than 0.425 mm (40 mesh), and 15 wt% or less of the granular activated carbon have a particle size higher than 1.70 mm (12 mesh).

16. The process according to claim 15, wherein 5 wt% or less, preferably 4 wt% or less, of the particle size is lower than 0.425 mm (40 mesh); and 10 wt% or less, preferably 5 wt% or less, of the particle size is higher than 1.70 mm (12 mesh).

17. The process according to any one of claims 1 to 16, wherein activated carbon is made of at least 50% coal, preferably of at least 70% coal, more preferably of at least 80% coal, and even more preferably of 90% coal.

18. The process according to any one of claims 1 to 17, wherein, after the deiodination step b), the activated carbon is re-used in step a).

19. The process according to any one of claims 1 to 18, wherein step b) is carried out by contacting the iodine-containing aromatic compound adsorbed onto the activated carbon with copper ions and OH- ions.

20. The process according to claim 19, wherein the amount of OH- ions is 0.5 moles or higher, per moles of adsorbed organic iodine.

21. The process according to claim 20, wherein the amount of OH- ions is 1 mole or higher per moles of adsorbed organic iodine.

22. The process according to claim 21, wherein the amount of OH- ions is 1 to 30 moles per moles of adsorbed organic iodine.

23. The process according to claim 22, wherein the amount of OH- ions is 1.5 to 10 moles per moles of adsorbed organic iodine.

24. The process according to claim 23, wherein the amount of OH- ions is 2 to 6 moles per moles of adsorbed organic iodine.

25. The process according to any one of claims 19 to 24, wherein copper ions are Cu2+ions.

26. The process according to claim 25, wherein the amount of Cu2+ions is catalytic.

27. The process according to claim 26, wherein the amount of Cu2+ions is at least 0.0001 moles per moles of adsorbed organic iodine.

28. The process according to claim 27, wherein the amount of Cu2+ions is at least 0.0002 moles per moles of adsorbed organic iodine.

29. The process according to claim 28, wherein the amount of Cu2+ions is at least 0.0004 moles per moles of adsorbed organic iodine.

30. The process according to claim 29, wherein the amount of Cu2+ions is 0.0008 moles per moles of adsorbed organic iodine.

31. The process according to any one of claims 19 to 30, wherein step b) is carried out at a temperature of 100 °C or higher.

32. The process according to claim 31, wherein step b) is carried out at a temperature of 110 °C or higher.

33. The process according to claim 32, wherein step b) is carried out at a temperature of 120 °C or higher.

34. The process according to any one of claims 19 to 33, wherein step b) is carried out for a time of 1 hour or more.

35. The process according to claim 34, wherein step b) is carried out for a time of 10 hours or more36. The process according to claim 35, wherein step b) is carried out for a time of 20 hours or more.

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