Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-09-13
2002-04-30
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S683000, C423S501000
Reexamination Certificate
active
06379556
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the recovery of iodide from chemical process wastewater. More particularly, the process of the invention involves a two-stage ion-exchange system comprising a strongly basic anionic resin and a weakly basic anionic resin for iodide recovery from wastewater, such as the wastewater resulting from the manufacture of indinavir sulfate, the active ingredient of the HIV protease inhibitor CRIXIVAN®.
BACKGROUND OF THE INVENTION
The recovery of expensive reagents from chemical process wastewater has been known to be an important factor in process economics for years and more recently known to be mandatory for environmental protection. More particularly, there has been considerable interest in and effort devoted to the recovery of iodide, because iodide is a relatively expensive material of limited availability, and, from an environmental perspective, because iodide is known to be toxic to certain fresh water aquatic organisms at very low concentrations (e.g., less than 1 mg/L). The recovery of iodide using anion exchange resin technology has been problematic, because iodide has a strong affinity for anionic exchange resins and the resin-bound iodide has been difficult to desorb, resulting thereby in unsatisfactory iodide recovery and in the loss of resin activity due to iodide enrichment.
Much of the iodide recovery effort has been directed to the isolation of iodide from low-concentration sources (<1 g/L) such as sea water. In those cases in which ion-exchange technology was used, desorption was attempted with alkali and found to offer inadequate recovery of iodide. Accordingly, oxidation of the iodide to free iodine was resorted to followed by reduction to iodide. This process was accompanied by all the safety and handling problems associated with free iodine. For example, Yamaguchi et al. disclose in Japanese Published Application No. JP 92-350078 a process of oxidizing or reducing an effluent which contains iodine and/or inorganic iodine compounds, followed by allowing the free iodine so formed to be adsorbed by a strongly basic anionic exchange resin which had adsorbed ionic iodine under acidic conditions. The adsorbed iodine is then allowed to react with sodium bisulfite and/or sodium sulfite and/or sodium hydroxide solution which results in elution of hydriodic acid. This is oxidized under acidic conditions and the free iodine obtained is purified by conventional procedures.
SUMMARY OF THE INVENTION
The present invention is a process which employs a two-stage anion-exchange method for recovery of up to about 99% of iodide present in chemical process wastewater as an aqueous solution of an iodide salt, typically an alkali metal iodide salt such as NaI. The process of the invention is suitable for use with chemical process wastewaters having very low to very high concentrations of iodide (e.g., from less than about 0.1 g/L to more than about 100 g/L), and optionally also contaminated with organic compounds, including solvents, and other inorganic ions. The anion-exchange resins suffer little or no loss of activity in the process due to iodide enrichment and thus can be re-used. The resulting iodide salt typically has sufficient purity to permit its re-use as a reagent in the chemical process. Importantly, the process of the present invention does not require oxidation/reduction and does not require the use of any expensive or toxic chemicals (i.e., the process can effectively employ readily available, inexpensive acids and bases). The use of relatively inexpensive chemicals in the process of the invention, combined with the ability to re-use the iodide salt recovered via the process, provides a significant economic advantage over conventional recovery processes which convert iodide to iodine. Furthermore, because the process of the invention can recover a substantial proportion of the iodide from the wastewater, it provides a significant environmental benefit.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a process for recovering iodide from chemical process wastewater which comprises:
(A) treating the wastewater containing iodide, and optionally other inorganics and organics, with a strongly basic anion-exchange resin in free-base form and washing the resin with aqueous solvent to remove materials not sorbed on the resin;
(B) treating the strongly basic resin with aqueous strong acid to desorb the iodide as HI;
(C) passing the HI solution from Step B through a weakly basic anion-exchange resin in free-base form and washing the resin with aqueous solvent to remove unsorbed materials; and
(D) treating the weakly basic resin with aqueous base to desorb the iodide as an iodide salt.
In a preferred embodiment, the process of the invention further comprises (E1) regenerating the desorbed weakly basic resin by washing with aqueous solvent. Step E1 permits re-use of the resin in step C of the process.
In another preferred embodiment, the process of the invention further comprises (E2) regenerating the desorbed strongly basic resin by washing the resin with aqueous base and then with aqueous solvent. Step E2 permits re-use of the resin in step A of the process.
In still another preferred embodiment, the process of the invention further comprises step E1 and step E2 as respectively set forth above.
In Step A, the strongly basic anion exchange resin in free-base form is suitably a polymer functionalized to contain quaternary ammonium groups, which groups are characterized by not readily associating with hydroxide ions in aqueous media, in analogy with the behavior of strong bases such as NaOH. As a result, the strongly basic resin can function over the entire pH range. The strongly basic resin is highly dissociated and sorbs or separates essentially all anionic species. The selectivity preference ranking of strongly basic resins for common anions is SO
4
=
>I
−
>NO
3
−
>Br
−
>Cl
−
>OH
−
. Suitable strongly basic anion-exchange resins include, but are not limited to, Amberlites IRA 400, IRA-410, IRA-402, IRA-458 and IRA-440c, all from Rohm & Haas. Amberlite IRA 400 is the preferred resin.
IRA 400 is an anion exchange resin with quaternary ammonium functionality in the chloride or hydroxide form, and has a porous gel bead structure based on a styrene divinylbenzene copolymer. IRA 400 consists of spherical particles and has an effective size of about 450 &mgr;m and a total exchange capacity of 1.4 meq/mL wet. IRA-402 resin has a quaternary ammonium functionality in the chloride form and is chemically the same as IRA-400, but with lower crosslinkage and more porosity. IRA-440c is another gel resin having a styrene divinylbenzene copolymer structure and quaternary ammonium functionality, with characteristics similar to IRA-400, but having tight particle size control (effective size=about 500 &mgr;m). IRA-458 is an acrylic divinyl benzene strongly basic anionic gel resin in the chloride form. IRA-458 has a particle size of about 470 &mgr;m and a total exchange capacity of 1.2 meq/mL wet. IRA-410 is an anion exchange resin having a styrene divinylbenzene copolymer structure with dimethylethanolamine functionality (chloride form), a particle size of about 480 &mgr;m, and a total exchange capacity of 1.4 meq/mL wet.
The resin is typically used in a column, although agitation with the wastewater in a vat, or other receptacle in batch mode, followed by filtration is also satisfactory. The resin column has a ratio of length/diameter of from about 2/1 to about 4/1, preferably from about 3/1 to about 4/1 (e.g., about 3/1). The wastewater flow rate through the resin column is typically in the range of from about 2 to about 40 mL/min/cm
2
(from about 0.5 to about 10 gal/min/ft
2
) of column cross-section, and preferably from about 4 to about 20 mL/min/cm
2
(from about 1 to about 5 gal/min/ft
2
) of column cross-section.
The resin with the sorbed iodide is washed with a volume of aqueous solvent at least about equal to the volume of wastewater loaded onto the resin
Magliette Ralph J.
McKinney Donald
Michaels Alan S.
Venkat Ed
Cintins Ivars
Merck & Co. , Inc.
Walton Kenneth R.
Winokur Melvin
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