STABILIZATION OF SUBSTITUTED 8-HYDROXYQUINOLINE HYDROMETALLURGICAL REAGENTS

Abstract: Method for substantially maintaining the loading capacity of a 7-(//c-alkenyl)-substituted 8-hydroxyquinoline hydrometallurgical reagent which comprises reducing the //c-alkenyl unsaturation while minimizing the saturation of the hydroxyquinoline group.

Description: . . STABILIZATION OF SUBSTITUTED 8-HYDROXYQUINOLINE HYDROMETALLURGICAL REAGENTS Background of the Invention The present invention relates to substituted 8-hydroxyquinoline hydromet lurgical reagents useful in selective solvent extraction of metal values from aqueous solution thereof and more particularly to a method for stabilizing s reagent for maintaining its loading capacity during such solvent extraction proces Subtituted 8-hydroxyquinoline reagents, such as disclosed in U. S. Patents 4,045,441 and 4,066,652, have been shown to be effective in extracting metal val (ions) from aqueous solutions thereof by a solvent extraction process. Briefly, su solvent extraction process comprises contacting the aqueous solution of the me with a hydrocarbon solvent containing the reagent followed by separation of t resulting organic and aqueous phases. The organic phase containing the met reagent complex or chelate then is contacted with an aqueous acidic strippi solution in order to concentrate the metal values in the acidic aqueous phase and regenerate the reagent in the organic solvent phase. By judicious selection process conditions, desirable metal values can be selectively separated and conce trated from other metal values by this process. While such hydrometallurgical reagents typically have an acceptable init loading capacity for the desired metal values to be recovered, the loading capaci of the reagent significantly declines and protracted phase separation times a experienced as the process proceeds with continual regeneration of the reage Accordingly, an effective method for stabilizing such substituted 8-hydroxyquinoli reagents for substantially maintaining the loading capacity thereof is needed. Broad Statement of the Invention The present invention is directed to a method for substantially maintaining t loading capacity of a 7-(c -alkenyl)-substituted 8-hydroxyquinoline hydrometa lurgical reagent. Such method comprises reducing theC --_U<enyl unsaturation whi minimizing the saturation of the hydroxyquinoline group thereof. Another aspe of the invention is directed to the use of such stabilized substituted 8-hydroxy quinoline reagent in a process for the selective recovery of one metal from the dilute aqueous solution of two or more metals wherein the aqueous solution is intimately contacted with the hydrocarbon solvent containing the stabilized reagent dissolved therein to provide a metal-reagent chelate in the solvent. The chelate- containing solvent then is intimately contacted with an aqueous acidic stripping solution to provide an aqueous phase containing the desired metal values and the solvent phase containing the regenerated reagent. Advantages of the present invention include the ability to substantiall maintain the initial loading capacity of the substituted 8-hydroxyquinoline hydro- metallurgical reagent during the selective solvent extraction process. Another advantage is that the stabilized substituted o<-hydroxyquinolme reagent retains the other advantages which they have in the process. These and other advantages wil become readily apparent to those skilled in the art based upon the disclosure herei contained. Brief Description of the Drawings The drawings depict graphically the results obtained in the examples and wil be described in detail in connection therewith. Detailed Description of the Invention The 7-C*X--_.kenyl)-substituted 8-hydroxyquinoline reagents of the presen invention preferably are those shown and described in U.S. Patent No. 4,045,441 an 4,066,652, the disclosures of which are expressly incorporated herein by reference. Such reagents contain unsaturation in the Of ,-(3 -position of the side chain attache in the 7 position to the 8-hydroxyquinoline group, which side chain unsaturation i reduced according to the precepts of the present invention. Preparation of thes unsaturated reagents can be practiced according to the teachings of said patents. The unsaturated reagents which are reduced according to the present invention ca be represented conventionally by the following general structural formulae: OMPI where 1} R„, R„, R 4 are alkyl groups, the sum total of carbon atoms in R.^ and being between 6 and 18 and in R„ and R . being between 4 and 18. Saturation of the (3 -, or ζ -alkyl branched© -unsaturated side chain attach to the 8-hydroxyquinoline unit stabilizes the reagent in the solvent extracti circuit. The saturated reagents can be represented by the following structures: OH Such stability is adjudged by and reflected in the loading capacity of the saturat reagent (the 8-hydroxyquinoline reagent substituted with a saturated alkyl group the 7 position) being substantially maintained for extended periods of time where the reagent is recirculated in the solvent extraction circuit. The instabili displayed by the unsaturated reagent (reagent of structure I or II) is believed to primarily caused by an oxidative cyclization reaction evidenced by large increases i furoquinoline being formed. When the unsaturation in the side chain is reduced, th proportion of such saturated reagent remains substantially constant in the circu and substantially no increase in furoquinoline by-product is noted. The drawings an the examples will further elaborate on this. Q..-7- Saturation of the side chain of the unsaturated reagent is accomplished by reduction of the double bond therein with hydrogen most preferably under conditions substantially preelusive of reducing the unsaturation in the rings of the 8- hydroxyquinoline substituent of the reagent. While a variety of agents (or catalysts) can be envisioned for the reduction reaction, most simply the unsaturated reagent is selectively hydrogenated in the presence of a selective hydrogenation catalyst. Selective hydrogenation for present purposes connotes saturation or reduction of the double bond in the side chain without substantially hydrogenating or reducing the unsaturation in the rings of the 8-hydroxyquinoline group. A wide variety of catalysts are useful for reducing the side chain of the unsaturated reagent by a conventional catalyzed hydrogenation process. Some observations on judicious selection of the catalyst, though, are important in this context. Because the unsaturated reagent is an effective ehelating reagent, use of homogeneous catalysts probably is not practical as the unsaturated reagent can chelate or complex readily therewith, thus, inactivating the catalyst. For the same reason, conventional heterogeneous divalent hydrogenation catalysts (e.g. Ni, Co, Cu, etc.) are not practical in the process. Advantageous catalysts for the process, then, can be selected from the supported and unsupported Group VHI metals having an atomic number of 44 or greater (e.g. Ru, Rh, Pd, Os, Ir, and Pt) and the Group vπb precious metal Re. These metals are fairly recalcitrant to being complexed ' by the unsaturated reagent in the selective hydrogenation process. The preferred catalyst for commercial implementation of the invention is a supported palladium catalyst. Carbon is the preferred support for the Pd catalyst, though alumina or other conventional support materials may be used in conventional fashion. Hydrogenation conditions for reducing the side chain of the reagent are conventional. Accordingly, advantageous hydrogenation temperatures range from about 60°-150°C, preferably about 90°-115°C, and advantageous hydrogen pressures range from about 60-400 psig, and preferably about 100-200 psig. It should be noted that intensive hydrogenation of the unsaturated reagent is not desirable as a practical matter because of the resultant difficulty in determining the end point of the hydrogenation reaction. Thus, for ease in controlling the degree of hydro¬ genation in the hydrogenation process, moderate conditions are preferable so that hydrogenation times in the range of around 2-4 hours will be experienced. Such moderate hydrogenation conditions and times permit GLC or other analytic techniques to be practiced during the hydrogenation process in order to control the O rl degree of hydrogenation of the unsaturated reagent. It should be understood however, that some saturation of the aromatic ring can occur even with the preferre Pd catalyst. For some reagents (e.g. reagent I with R 1 being a butyl group and R being an ethyl group) subjected to the reduction process, the degree of rin saturation in the final reagent product is sufficiently minimal that such rin saturation has no adverse effects in the extraction circuit as a practical matter. I required for the reagents, however, the rings can be rearomatized rather readily b mere heating of the reduced reagent in the presence of a dehy rogenation catalys (e.g. Pd or other hydrogenation catalyst, such as listed above) at a temperature o above about 220°C and advantageously between about 220° and 300°C. An inert ga sparge may be used in this rearomatization reaction, though such sparge is no necessary. The saturated reagents of the present invention find wide use in the solven extraction of metal values from aqueous solutions wherein the reagent is disperse in an organic solvent, as such process is disclosed in U.S. Patents Nos. 3,637,711, 4,045,441, 4,066,652, the disclosures of which are expressly incorporated herein b reference. Briefly, such process comprises mixing a dilute aqueous solution of the metal values, of which one of the metals is desired to be selectively separated from a mixture of metal values, with a hydrocarbon solvent containing the reagent dispersed therein. A promoter can be added to the hydrocarbon solvent. The presently preferred promoter is tridecyl alcohol. Other suitable promoters include isodecyl alcohol or other aliphatic alcohols (U. S. Pat. No. 3,224,873), alkylated phenols (U. S. Pat. No. 3,725,046), and other suitable conventional promoters. Upon mixing of the dilute aqueous phase and the organic solvent phase in a mixing- extraction tank, such mixture is permitted to settle for separation into two phases. The organic phase containing the metal-reagent chelate then is contacted with an acidic aqueous stripping solution under suitable mixing or agitation conditions. This mixture then is permitted to settle for formation of an organic phase containing the regenerated reagent for recycle and an acidic aqueous phase containing the metal values which have been selectively separated by the process. The metal value of choice to be separated by the reagents of the present invention is copper, though a wide variety of metals can be separated by the reagents, as such metal values are set forth in U.S. Patent No. 3,637,711. Further specific polyvalent metals which can be separated by the reagents of the present invention include, for example, rare earth metals and yttrium (European Patent Application S.N. 79400120.6, filed February 27, 1979, of Rhone-Poulenc Industries, Paris, France); gallium (U. S. Pat. No. 3,971,843); and copper, zinc and nickel (Ritcey et al, "Evaluation of Contactors for the Extraction and Separation o Copper, Zinc, and Nickel from Ammoniacal Solutions Using Kelex 100," I. Chem E Symposium Series No. 42, and Hartlage et al, "Kele (R) Copper Extraction: A Stud of the Stripping Mechanism," I. Chem. E. Symposium Series No. 42, pp. 12.1-12.9 an 13.1-13.7, respectively, 1975). Representative organic solvents which can be used i the process include benzene, toluene, xylene, fuel oil, and a wide variety of othe hydrocarbons, but preferably kerosene. Conditions obtaining during the extractio process (eg. temperature, pH, and the like) are conventional and can be found in th various citations referred to above. The following examples show how the present invention can be practiced bu should not be construed as limiting. In this application, all units are in the metri system unless otherwise expressly indicated. Also, all citations noted herein ar expressly incorporated herein by reference. IN THE EXAMPLES The unsaturated reagent evaluated can be represented by the formula: and was made in a procedure substantially as described in Example 1 of U.S. Paten No. 4,045,441. The theoretical loading capacity of this reagent for copper (Cu 2+ ) i 1.07. Extensive testing indicated that laboratory prepared samples of this reagen had loading capacities generally ranging from 0.70 to 0.95 gpl. and pilot plan prepared samples had loading capacities of 0.82 to 0.87 gpl. Loading capacities are determined by a standard control method by extractin copper from a standard solution and measuring the amount of copper in the aqueou phase before and after extraction. The loading capacity of the reagent is th difference in the amount of copper in the aqueous phase before and after extractio and is expressed in grams per liter (gpl). The standard control method uses a 1% (weight/volume) of the reagent i kerosene (Escaid 200) containing 15% by weight nonyl phenol. 650 ml of the reagen solution is washed twice with 300 ml each of a sulfuric acid solution (200 gms o H 2 SO . diluted to 1 liter with distilled water) in order to ensure that no metal value • ^U _-J-^'- are therein. The washed reagent solution (50 ml) is mixed with a standard coppe solution (21.6 gms of CuSO 4 "5H 2 0 diluted to 1 liter with distilled water and p adjusted with additional H 2 SO 4 to 3.0+0.2), the two layers permitted to settle, an the two layers separated. This extraction step is repeated and the two resultin aqueous phases combined. Copper determinations are made by adding 10 ml of a potassium iodide solutio (150 gms KI diluted with distilled water to 1 L) to the. standard copper solution an to the combined aqueous phases. The two resulting solutions then are titrate separately with 0.1 N sodium thiosulfate solution to a light yellow color, a solubl starch indicator added, and 'titration continued until the blue color just disappear and remains so for 30 seconds. The copper concentration (gpl) is calculated for eac solution by dividing the milliliters of the sample by the product of the milliliters o the titrating solution times its normality times a constant of 63.5. The loadin capacity of the reagent is the difference between the copper concentration in th standard and the combined phases multiplied by 2. Reduction of the reagent was accomplished by charging a reactor with th unsaturated reagent (V) and 0.4% by weight of a wet 5% palladium on carbon (50 H„0 and 50% of 5% Pd/C) catalyst and purging the air from the reactor. Th contents of the .reactor were heated to about 125 C under 60 psig of hydrogen gas Samples of the reagent were removed periodically and analyzed by GLC (gas-liqui chromatrography) in order to determine the progress of the reduction reaction. Ful reduction of the side chain occurs in about 2-4 hours. In order to dehydrogenate th partially hydrogenated quinoline group, the reactor was vented of all H„, and heate up to a final temperature of about 250°C. At about 190°C, hydrogen begins t evolve from the reduced reagent. The evolved H 2 is vented from the reactor whic is maintained at about 250 C for about 2-3 hours until samples of the reagent indicate that the dehydrogenation reaction is complete. Conveniently, the dehydro- genation reaction can be considered complete when the reagent regains a loading capacity which is at least 95% of its pre-reduction loading capacity. EXAMPLE 1 The unsaturated reagent (V) used in this example had an initial loading capacity of 0.87. Pilot plant extraction of copper with the reagent showed that after 45 hours in the circuit, the loading capacity had dropped to 0.77 (an 11.5% loss of loading capacity). Accordingly, reduction of the side chain unsaturation was tried as a method of reestablishing the initial loading capacity of the unsaturated reagent. - 8 - In order to generate data points on loading capacity and phase separatio times of the organic phase (kerosene, nonyl phenol and reagent) from the aqueou copper solution, the reduction of the reagent was continued until substantial rin reduction had occurred. GLC analysis of the reagent also was conducted. Th results of these tests are displayed in Figs. 1 and 2. Fig. 1 depicts graphically the loading capacity of the reagent and phas separation time as a function of the reduction time. The linear loss of loadin capacity shows no sign of leveling off and phase separation times have increase substantially. Figs. 2A and 2B depict the results of GLC analysis of samples of the reagen as a function of reduction time. From Fig. 2A it can be seen that the proportion o reduced reagent increases with increasing reduction time and that two unsaturate components of the reagent decrease with increasing reduction time. Fig. 2B show that furoquinoline by-product in the reagent is converted to a reduced form als Since no degradation or generation of a non-copper loading species is evidenced i the GLC analysis, the GLC analysis was modified to split the reduced reagen component into two components. The second component was theorized to be th ring-reduced analogue of the saturated reagent. This was confirmed by dehydro genating the final reduced reagent (250 C for 3-4 hours in the presence of the Pd o carbon catalyst) which restored the loading capacity of the reagent to within 95% o its initial loading capacity. Three components isolated from the reduced reagent by fractional distillatio on a spinning band column were analyzed by a combination of NMR (nuclea magnetic resonance) and GC-MS (gas chromatography-mass spectrometry). Th saturated reagent and furoquinoline were confirmed by such analysis. The thir component is believed to be dϊhydrofuroquinoline because all of the furoquinolin was converted to this third component under total reduction conditions. The tw unsaturated components in the reagent are believed to be two isomeric forms of th unsaturated reagent wherein the side chain unsaturation is either in the chain a shown for reagent A (structure (V)) or is pendant to the chain as shown below fo reagent B (Structure (VI)): OH . - 9 - It should be understood that the precise structures for the two isomeric forms of t unsaturated reagent shown herein are merely the most likely structures based current information and are not a limitation on the present invention as reduction the unsaturation in either position will result in the saturated reagent of the prese invention. Thus, it appears as though the unsaturated reagent actually is a mixtu of two (or more) isomeric forms thereof. EXAMPLE 2 In order to evaluate the stability of the reagents, an accelerated circu variation test was devised. The reagent being evaluated was mixed continuous with a stripping electrolyte solution (150 gpl of H„SO . and 30 gpl of Cu 2+ 2 S0 4 in wate at 45 -50 C. Periodic samples of the reagent were examined for loading capaci and compositional changes by GLC, The reagent was a mixture of the unsaturat reagent, the side chain-saturated reagent, and furoquinoline. Two circuit runs we conducted on the partially reduced reagent, one being in the presence of air and t other being under an inert nitrogen blanket. The total test time was 382 hours. T proportions of each component in the reagent mixture for each circuit run is give in Figs. 3 and 4. Fig. 3 depicts the results of the test conducted in air graphically by plottin the concentration of the components in the reagent as a function of time. Note th the unsaturated reagent components concentration decreases during the course the circuit test. Fig. 4 depicts the results of the nitrogen atmosphere tests. Not that the concentration of the unsaturated components is substantially maintaine It appears that the unsaturated reagents instability is primarily an oxidativ cyclization process evidenced by the large increase in furoquinoline in Fig. 3. Not however, that the saturated reagent is stable both in air (Fig. 3) and in nitrogen (Fig. 4) and that substantially no increase in furoquinoline is evidenced for the nitrogen ru (Fig. 4).

Claims: CLAIMS 1. A method for substantially maintaining the loading capacity of a 7-{o alkenyD-substituted 8-hydroxyquinoline reagent for removing polyvalent metal io 5 from a mixture of metal ions in a dilute aqueous solution thereof and f regenerating said substituted 8-hydroxyquinoline from the resulting metal compl thereof, which comprises reducing said c<-alkenyl unsaturation while minimizing t saturation of said hydroxyquinoline group. 2. The method of claim 1 wherein saido<-alkenyl unsaturation is reduced 10 selective hydrogenation in the presence of a selective hydrogenation catalyst wi hydrogen gas under selective hydrogenation conditions. 3. The method of claim 2 wherein any hydrogen added to said hydrox quinoline group is removed by dehydrogenation thereof. 4. The method of claim 2 wherein said catalyst is a Group VHb or Group VI 15 metal having an atomic number of between 43 and 78.. 5. The method of claim 2 wherein said hydrogenation catalyst is palladium 6. The method of claim 5 wherein said palladium is disposed on an ine support. 7. The method of claim 6 wherein said support is carbon. 20 8. The method of claim 2 or 5 wherein said hydrogenation conditio include a temperature of between about 60° and 150°C and a pressure of betwe about 60 and 400 psig. 9. The method of claim 3 wherein said dehydrogenation is conducted in t presence of said hydrogenation catalyst at a temperature of between about 220° a 25 300°C. 10. The method of claim 9 wherein said catalyst is palladium disposed on inert support. j - ' - J t- - 11 - 11. The method- of claim 1 or 10 wherein said 7-(c -alkenyl)-substituted hydroxyquinoline has the formula or where R_ , R„, R,, R 4 are alkyl groups, the sum total of carbon atoms in R and R„ being between 6 and 18 and in R, and 4 being between 4 and 18. 12. The method of claim 11 wherein said reagent is of formula (I) and has R being a butyl group and R 2 being an ethyl group. 13. The method of claim 11 wherein said reagent is of formula (π) and ha R„ being a 2-ethylhexyl group and R 4 being an ethyl group. 14. In a process for the recovery of polyvalent metal values from a dilut aqueous solution thereof wherein said aqueous solution is intimately contacted wit a hydrocarbon solvent containing a chelation reagent dispersed therein to provide polyvalent metal-reagent chelate in said solvent, said chelate-containing solven being intimately contacted with an aqueous acidic stripping solution to provide a aqueous phase containing said polyvalent metal values and said reagent regenerate in said solvent, the improvement which comprises using a chelation agent having th formula or OH where R., , R«, R-, R 4 are alkyl groups, the sum total of carbon atoms in R and R» being between 6 and 18 and in „ and R 4 being between 4 and 18. 15. The method of claim 14 wherein said reagent used is of formula (HI) a has R. being a butyl group and R„ being an ethyl group. 16. The method of claim 14 wherein said reagent used is of formula (IV) an has R„ being a 2-ethylhexyl group and 4 being an ethyl group. 17. The method of claim 14 wherein said hydrocarbon solvent contains a alkylated phenol or an aliphatic primary alcohol promoter, the volumetric ratio said reagent to said promoter being between about 1:19 and 1:1. 18. The method of claim 17 wherein said promoter is tridecyl alcohol. 19. The method of claim 14 or 18 wherein said hydrocarbon solvent kerosene. • ^ϋ ' _.-.£ c .?ι

Inventors: GEFVERT DAVID L, RICHARDS HARVEY J
Applicants: SHEREX CHEM, SHEREX CHEM CO
Application year: 1981
Main classification: C07D217
IPC codes: C07D215, C22B3